diff --git a/src/classes/PMsrHandler.cpp b/src/classes/PMsrHandler.cpp
index 0d6326265..50c71a9dc 100644
--- a/src/classes/PMsrHandler.cpp
+++ b/src/classes/PMsrHandler.cpp
@@ -2874,15 +2874,13 @@ Bool_t PMsrHandler::HandleFitParameterEntry(PMsrLines &lines)
       param.fName = tokens[1].c_str();
 
       // parameter value
-      if (PStringUtils::IsFloat(tokens[2]))
-        param.fValue = PStringUtils::ToDouble(tokens[2]);
-      else
+      param.fValue = PStringUtils::ToDouble(tokens[2], &ok);
+      if (!ok)
         error = true;
 
-      // parameter value
-      if (PStringUtils::IsFloat(tokens[3]))
-        param.fStep = PStringUtils::ToDouble(tokens[3]);
-      else
+      // parameter step
+      param.fStep = PStringUtils::ToDouble(tokens[3], &ok);
+      if (!ok)
         error = true;
 
       // 4 values, i.e. No Name Value Step
@@ -2895,14 +2893,13 @@ Bool_t PMsrHandler::HandleFitParameterEntry(PMsrLines &lines)
         param.fNoOfParams = 5;
 
         // positive error
-        if (PStringUtils::IsFloat(tokens[4])) {
+        param.fPosError = PStringUtils::ToDouble(tokens[4], &ok);
+        if (ok) {
           param.fPosErrorPresent = true;
-          param.fPosError = PStringUtils::ToDouble(tokens[4]);
+        } else if (PStringUtils::IsEqualNoCase(tokens[4], "none")) {
+          param.fPosErrorPresent = false;
         } else {
-          if (PStringUtils::IsEqualNoCase(tokens[4], "none"))
-            param.fPosErrorPresent = false;
-          else
-            error = true;
+          error = true;
         }
       }
 
@@ -2911,14 +2908,13 @@ Bool_t PMsrHandler::HandleFitParameterEntry(PMsrLines &lines)
         param.fNoOfParams = 7;
 
         // positive error
-        if (PStringUtils::IsFloat(tokens[4])) {
+        param.fPosError = PStringUtils::ToDouble(tokens[4], &ok);
+        if (ok) {
           param.fPosErrorPresent = true;
-          param.fPosError = PStringUtils::ToDouble(tokens[4]);
+        } else if (PStringUtils::IsEqualNoCase(tokens[4], "none")) {
+          param.fPosErrorPresent = false;
         } else {
-          if (PStringUtils::IsEqualNoCase(tokens[4], "none"))
-            param.fPosErrorPresent = false;
-          else
-            error = true;
+          error = true;
         }
 
         // lower boundary
@@ -2926,8 +2922,8 @@ Bool_t PMsrHandler::HandleFitParameterEntry(PMsrLines &lines)
         if (PStringUtils::IsEqualNoCase(tokens[5], "none")) { // none
           param.fLowerBoundaryPresent = false;
         } else { // assuming that the lower boundary is a number
-          if (PStringUtils::IsFloat(tokens[5])) {
-            param.fLowerBoundary = PStringUtils::ToDouble(tokens[5]);
+          param.fLowerBoundary = PStringUtils::ToDouble(tokens[5], &ok);
+          if (ok) {
             param.fLowerBoundaryPresent = true;
           } else {
             error = true;
@@ -2939,8 +2935,8 @@ Bool_t PMsrHandler::HandleFitParameterEntry(PMsrLines &lines)
         if (PStringUtils::IsEqualNoCase(tokens[6], "none")) { // none
           param.fUpperBoundaryPresent = false;
         } else { // assuming a number
-          if (PStringUtils::IsFloat(tokens[6])) {
-            param.fUpperBoundary = PStringUtils::ToDouble(tokens[6]);
+          param.fUpperBoundary = PStringUtils::ToDouble(tokens[6], &ok);
+          if (ok) {
             param.fUpperBoundaryPresent = true;
           } else {
             error = true;
@@ -3125,11 +3121,10 @@ Bool_t PMsrHandler::HandleGlobalEntry(PMsrLines &lines)
       if (tokens.size() < 3) {
         error = true;
       } else {
-        if (PStringUtils::IsFloat(tokens[1])) {
-          dval = PStringUtils::ToDouble(tokens[1]);
-          if (dval <= 0.0)
-            error = true;
-        }
+        bool ok = false;
+        dval = PStringUtils::ToDouble(tokens[1], &ok);
+        if (!ok || dval <= 0.0)
+          error = true;
         if (!error) {
           global.SetRRFFreq(dval, tokens[2].c_str());
           if (global.GetRRFFreq(tokens[2].c_str()) == RRF_FREQ_UNDEF)
@@ -3152,12 +3147,12 @@ Bool_t PMsrHandler::HandleGlobalEntry(PMsrLines &lines)
       if (tokens.size() < 2) {
         error = true;
       } else {
-        if (PStringUtils::IsFloat(tokens[1])) {
-          dval = PStringUtils::ToDouble(tokens[1]);
+        bool ok = false;
+        dval = PStringUtils::ToDouble(tokens[1], &ok);
+        if (ok)
           global.SetRRFPhase(dval);
-        } else {
+        else
           error = true;
-        }
       }
     } else if (iter->fLine.BeginsWith("data", TString::kIgnoreCase)) { // data
       if (tokens.size() < 3) {
@@ -3178,15 +3173,12 @@ Bool_t PMsrHandler::HandleGlobalEntry(PMsrLines &lines)
         error = true;
       } else {
         for (UInt_t i=1; i<tokens.size(); i++) {
-          if (PStringUtils::IsFloat(tokens[i])) {
-            dval = PStringUtils::ToDouble(tokens[i]);
-            if (dval >= 0.0)
-              global.SetT0Bin(dval);
-            else
-              error = true;
-          } else {
+          bool ok = false;
+          dval = PStringUtils::ToDouble(tokens[i], &ok);
+          if (ok && dval >= 0.0)
+            global.SetT0Bin(dval);
+          else
             error = true;
-          }
         }
       }
     } else if (iter->fLine.BeginsWith("addt0", TString::kIgnoreCase)) { // addt0
@@ -3194,15 +3186,12 @@ Bool_t PMsrHandler::HandleGlobalEntry(PMsrLines &lines)
         error = true;
       } else {
         for (UInt_t i=1; i<tokens.size(); i++) {
-          if (PStringUtils::IsFloat(tokens[i])) {
-            dval = PStringUtils::ToDouble(tokens[i]);
-            if (dval >= 0.0)
-              global.SetAddT0Bin(dval, addT0Counter, i-1);
-            else
-              error = true;
-          } else {
+          bool ok = false;
+          dval = PStringUtils::ToDouble(tokens[i], &ok);
+          if (ok && dval >= 0.0)
+            global.SetAddT0Bin(dval, addT0Counter, i-1);
+          else
             error = true;
-          }
         }
       }
       addT0Counter++;
@@ -3241,8 +3230,10 @@ Bool_t PMsrHandler::HandleGlobalEntry(PMsrLines &lines)
             global.SetFitRangeInBins(true);
         } else { // fit given in time, i.e. fit <start> <end>, where <start>, <end> are given as doubles
           for (UInt_t i=1; i<3; i++) {
-            if (PStringUtils::IsFloat(tokens[i]))
-              global.SetFitRange(PStringUtils::ToDouble(tokens[i]), i-1);
+            bool ok = false;
+            const double range = PStringUtils::ToDouble(tokens[i], &ok);
+            if (ok)
+              global.SetFitRange(range, i-1);
             else
               error = true;
           }
@@ -3641,8 +3632,10 @@ Bool_t PMsrHandler::HandleRunEntry(PMsrLines &lines)
         error = true;
       } else {
         for (UInt_t i=1; i<tokens.size(); i++) {
-          if (PStringUtils::IsFloat(tokens[i]))
-            param.SetBkgFix(PStringUtils::ToDouble(tokens[i]), i-1);
+          bool ok = false;
+          const double bkgFix = PStringUtils::ToDouble(tokens[i], &ok);
+          if (ok)
+            param.SetBkgFix(bkgFix, i-1);
           else
             error = true;
         }
@@ -3696,15 +3689,12 @@ Bool_t PMsrHandler::HandleRunEntry(PMsrLines &lines)
         error = true;
       } else {
         for (UInt_t i=1; i<tokens.size(); i++) {
-          if (PStringUtils::IsFloat(tokens[i])) {
-            dval = PStringUtils::ToDouble(tokens[i]);
-            if (dval >= 0.0)
-              param.SetT0Bin(dval);
-            else
-              error = true;
-          } else {
+          bool ok = false;
+          dval = PStringUtils::ToDouble(tokens[i], &ok);
+          if (ok && dval >= 0.0)
+            param.SetT0Bin(dval);
+          else
             error = true;
-          }
         }
       }
     }
@@ -3718,15 +3708,12 @@ Bool_t PMsrHandler::HandleRunEntry(PMsrLines &lines)
         error = true;
       } else {
         for (UInt_t i=1; i<tokens.size(); i++) {
-          if (PStringUtils::IsFloat(tokens[i])) {
-            dval = PStringUtils::ToDouble(tokens[i]);
-            if (dval >= 0.0)
-              param.SetAddT0Bin(dval, addT0Counter, i-1);
-            else
-              error = true;
-          } else {
+          bool ok = false;
+          dval = PStringUtils::ToDouble(tokens[i], &ok);
+          if (ok && dval >= 0.0)
+            param.SetAddT0Bin(dval, addT0Counter, i-1);
+          else
             error = true;
-          }
         }
       }
 
@@ -3773,8 +3760,10 @@ Bool_t PMsrHandler::HandleRunEntry(PMsrLines &lines)
             param.SetFitRangeInBins(true);
         } else { // fit given in time, i.e. fit <start> <end>, where <start>, <end> are given as doubles
           for (UInt_t i=1; i<3; i++) {
-            if (PStringUtils::IsFloat(tokens[i]))
-              param.SetFitRange(PStringUtils::ToDouble(tokens[i]), i-1);
+            bool ok = false;
+            const double range = PStringUtils::ToDouble(tokens[i], &ok);
+            if (ok)
+              param.SetFitRange(range, i-1);
             else
               error = true;
           }
@@ -4017,8 +4006,10 @@ Bool_t PMsrHandler::ParseFourierPhaseValueVector(PMsrFourierStructure &fourier,
 
   // convert all acceptable tokens
   for (UInt_t i=1; i<tok.size(); i++) {
-    if (PStringUtils::IsFloat(tok[i])) {
-      fourier.fPhase.push_back(PStringUtils::ToDouble(tok[i]));
+    bool ok = false;
+    const double phase = PStringUtils::ToDouble(tok[i], &ok);
+    if (ok) {
+      fourier.fPhase.push_back(phase);
     } else {
       result = false;
       if (i>1) { // make sure that no 'phase val, parX' mixture is present
@@ -4440,9 +4431,9 @@ Bool_t PMsrHandler::HandleFourierEntry(PMsrLines &lines)
         continue;
       } else {
         for (UInt_t i=0; i<2; i++) {
-          if (PStringUtils::IsFloat(tokens[i+1])) {
-            fourier.fPlotRange[i] = PStringUtils::ToDouble(tokens[i+1]);
-          } else {
+          bool ok = false;
+          fourier.fPlotRange[i] = PStringUtils::ToDouble(tokens[i+1], &ok);
+          if (!ok) {
             error = true;
             continue;
           }
@@ -4473,11 +4464,10 @@ Bool_t PMsrHandler::HandleFourierEntry(PMsrLines &lines)
       break;
     case 3:
       for (UInt_t i=0; i<2; i++) {
-        if (PStringUtils::IsFloat(tokens[i+1])) {
-          fourier.fRangeForPhaseCorrection[i] = PStringUtils::ToDouble(tokens[i+1]);
-        } else {
+        bool ok = false;
+        fourier.fRangeForPhaseCorrection[i] = PStringUtils::ToDouble(tokens[i+1], &ok);
+        if (!ok)
           error = true;
-        }
       }
       break;
     default:
@@ -4640,28 +4630,33 @@ Bool_t PMsrHandler::HandlePlotEntry(PMsrLines &lines)
         } else {
 
           // handle t_min
-          if (PStringUtils::IsFloat(tokens[1]))
-            param.fTmin.push_back(PStringUtils::ToDouble(tokens[1]));
+          bool ok = false;
+          const double tmin = PStringUtils::ToDouble(tokens[1], &ok);
+          if (ok)
+            param.fTmin.push_back(tmin);
           else
             error = true;
 
           // handle t_max
-          if (PStringUtils::IsFloat(tokens[2]))
-            param.fTmax.push_back(PStringUtils::ToDouble(tokens[2]));
+          const double tmax = PStringUtils::ToDouble(tokens[2], &ok);
+          if (ok)
+            param.fTmax.push_back(tmax);
           else
             error = true;
 
           if (tokens.size() == 5) { // y-axis interval given as well
 
             // handle y_min
-            if (PStringUtils::IsFloat(tokens[3]))
-              param.fYmin.push_back(PStringUtils::ToDouble(tokens[3]));
+            const double ymin = PStringUtils::ToDouble(tokens[3], &ok);
+            if (ok)
+              param.fYmin.push_back(ymin);
             else
               error = true;
 
             // handle y_max
-            if (PStringUtils::IsFloat(tokens[4]))
-              param.fYmax.push_back(PStringUtils::ToDouble(tokens[4]));
+            const double ymax = PStringUtils::ToDouble(tokens[4], &ok);
+            if (ok)
+              param.fYmax.push_back(ymax);
             else
               error = true;
           }
@@ -4681,14 +4676,17 @@ Bool_t PMsrHandler::HandlePlotEntry(PMsrLines &lines)
           for (UInt_t i=0; i<param.fRuns.size(); i++) {
 
             // handle t_min
-            if (PStringUtils::IsFloat(tokens[2*i+1]))
-              param.fTmin.push_back(PStringUtils::ToDouble(tokens[2*i+1]));
+            bool ok = false;
+            const double tmin = PStringUtils::ToDouble(tokens[2*i+1], &ok);
+            if (ok)
+              param.fTmin.push_back(tmin);
             else
               error = true;
 
             // handle t_max
-            if (PStringUtils::IsFloat(tokens[2*i+2]))
-              param.fTmax.push_back(PStringUtils::ToDouble(tokens[2*i+2]));
+            const double tmax = PStringUtils::ToDouble(tokens[2*i+2], &ok);
+            if (ok)
+              param.fTmax.push_back(tmax);
             else
               error = true;
           }
@@ -4697,14 +4695,17 @@ Bool_t PMsrHandler::HandlePlotEntry(PMsrLines &lines)
           if (tokens.size() == 2*param.fRuns.size() + 3) {
 
             // handle y_min
-            if (PStringUtils::IsFloat(tokens[2*param.fRuns.size()+1]))
-              param.fYmin.push_back(PStringUtils::ToDouble(tokens[2*param.fRuns.size()+1]));
+            bool ok = false;
+            const double ymin = PStringUtils::ToDouble(tokens[2*param.fRuns.size()+1], &ok);
+            if (ok)
+              param.fYmin.push_back(ymin);
             else
               error = true;
 
             // handle y_max
-            if (PStringUtils::IsFloat(tokens[2*param.fRuns.size()+2]))
-              param.fYmax.push_back(PStringUtils::ToDouble(tokens[2*param.fRuns.size()+2]));
+            const double ymax = PStringUtils::ToDouble(tokens[2*param.fRuns.size()+2], &ok);
+            if (ok)
+              param.fYmax.push_back(ymax);
             else
               error = true;
           }
@@ -4717,14 +4718,17 @@ Bool_t PMsrHandler::HandlePlotEntry(PMsrLines &lines)
 
         if (tokens.size() == 3) { // i.e. use_fit_ranges ymin ymax
           // handle y_min
-          if (PStringUtils::IsFloat(tokens[1]))
-            param.fYmin.push_back(PStringUtils::ToDouble(tokens[1]));
+          bool ok = false;
+          const double ymin = PStringUtils::ToDouble(tokens[1], &ok);
+          if (ok)
+            param.fYmin.push_back(ymin);
           else
             error = true;
 
           // handle y_max
-          if (PStringUtils::IsFloat(tokens[2]))
-            param.fYmax.push_back(PStringUtils::ToDouble(tokens[2]));
+          const double ymax = PStringUtils::ToDouble(tokens[2], &ok);
+          if (ok)
+            param.fYmax.push_back(ymax);
           else
             error = true;
         }
@@ -4761,11 +4765,10 @@ Bool_t PMsrHandler::HandlePlotEntry(PMsrLines &lines)
           error = true;
         } else {
           // get rrf frequency
-          if (PStringUtils::IsFloat(tokens[1])) {
-            param.fRRFFreq = PStringUtils::ToDouble(tokens[1]);
-          } else {
+          bool ok = false;
+          param.fRRFFreq = PStringUtils::ToDouble(tokens[1], &ok);
+          if (!ok)
             error = true;
-          }
           // get unit
           if (PStringUtils::ContainsNoCase(tokens[2], "kHz"))
             param.fRRFUnit = RRF_UNIT_kHz;
@@ -4788,25 +4791,25 @@ Bool_t PMsrHandler::HandlePlotEntry(PMsrLines &lines)
           error = true;
         } else {
           // get rrf phase
-          if (PStringUtils::IsFloat(tokens[1])) {
-            param.fRRFPhase = PStringUtils::ToDouble(tokens[1]);
-          } else {
-            if (PStringUtils::BeginsWithNoCase(tokens[1], "par")) { // parameter value
-              Int_t no = 0;
-              if (FilterNumber(tokens[1].c_str(), "par", 0, no)) {
-                // check that the parameter is in range
-                if (static_cast<Int_t>(fParam.size()) < no) {
-                  error = true;
-                } else {
-                  // keep the parameter number in case parX was used
-                  param.fRRFPhaseParamNo = no;
-                  // get parameter value
-                  param.fRRFPhase = fParam[no-1].fValue;
-                }
+          bool ok = false;
+          const double rrfPhase = PStringUtils::ToDouble(tokens[1], &ok);
+          if (ok) {
+            param.fRRFPhase = rrfPhase;
+          } else if (PStringUtils::BeginsWithNoCase(tokens[1], "par")) { // parameter value
+            Int_t no = 0;
+            if (FilterNumber(tokens[1].c_str(), "par", 0, no)) {
+              // check that the parameter is in range
+              if (static_cast<Int_t>(fParam.size()) < no) {
+                error = true;
+              } else {
+                // keep the parameter number in case parX was used
+                param.fRRFPhaseParamNo = no;
+                // get parameter value
+                param.fRRFPhase = fParam[no-1].fValue;
               }
-            } else {
-              error = true;
             }
+          } else {
+            error = true;
           }
         }
       } else if (iter1->fLine.Contains("rrf_packing", TString::kIgnoreCase)) {
diff --git a/src/classes/PStringUtils.cpp b/src/classes/PStringUtils.cpp
index 59c05cb88..45eaf89a7 100644
--- a/src/classes/PStringUtils.cpp
+++ b/src/classes/PStringUtils.cpp
@@ -28,6 +28,7 @@
  ***************************************************************************/
 
 #include <cctype>
+#include <cerrno>
 #include <charconv>
 #include <cstdlib>
 
@@ -161,12 +162,29 @@ int PStringUtils::ToInt(const std::string &str, bool *ok)
  * <p>Converts the leading part of the string to a double, mirroring
  * TString::Atof(). Returns 0.0 if no conversion is possible.
  *
+ * <p>Like ToInt(), conversion errors can be reported through the optional
+ * \a ok out-parameter: it is set to true when a value was parsed and to
+ * false otherwise (no number present, or the value is out of range). This
+ * lets callers distinguish a legitimate 0.0 from a failed conversion.
+ * strtod() (rather than std::from_chars) is used so that the accepted input
+ * set stays identical to TString::Atof() (leading whitespace is skipped, a
+ * leading '+' is honoured, trailing characters are ignored). A null \a ok
+ * preserves the historic fire-and-forget behaviour.
+ *
  * \param str string to be converted
- * \return converted double value
+ * \param ok  optional out-parameter signalling conversion success
+ * \return converted double value (0.0 on error)
  */
-double PStringUtils::ToDouble(const std::string &str)
+double PStringUtils::ToDouble(const std::string &str, bool *ok)
 {
-  return std::strtod(str.c_str(), nullptr);
+  const char *begin = str.c_str();
+  char *end = nullptr;
+  errno = 0;
+  const double value = std::strtod(begin, &end);
+  if (ok != nullptr)
+    *ok = (end != begin) && (errno != ERANGE);
+
+  return value;
 }
 
 //--------------------------------------------------------------------------
diff --git a/src/include/PStringUtils.h b/src/include/PStringUtils.h
index 3cc086c5a..c28aadc65 100644
--- a/src/include/PStringUtils.h
+++ b/src/include/PStringUtils.h
@@ -104,10 +104,15 @@ class PStringUtils
      * <p>Converts the leading part of the string to a double.
      * Mirrors TString::Atof(). Returns 0.0 if no conversion is possible.
      *
+     * <p>If \a ok is non-null it is set to true when a value was parsed and
+     * to false on error (no number, or value out of range), allowing callers
+     * to distinguish a legitimate 0.0 from a failed conversion.
+     *
      * @param str string to be converted
-     * @return converted double value
+     * @param ok  optional out-parameter signalling conversion success
+     * @return converted double value (0.0 on error)
      */
-    static double ToDouble(const std::string &str);
+    static double ToDouble(const std::string &str, bool *ok = nullptr);
 
     /**
      * <p>Case-insensitive full-string equality.