diff --git a/pvDataApp/factory/Convert.cpp b/pvDataApp/factory/Convert.cpp
index 7a43cd8..2633215 100644
--- a/pvDataApp/factory/Convert.cpp
+++ b/pvDataApp/factory/Convert.cpp
@@ -45,10 +45,7 @@ static std::vector<String> split(String commaSeparatedList) {
 }
     
 Convert::Convert()
-: pvDataCreate(getPVDataCreate()),
-  trueString("true"),
-  falseString("false"),
-  illegalScalarType("Illegal ScalarType")
+: pvDataCreate(getPVDataCreate())
 {}
 
 
@@ -298,8 +295,7 @@ void Convert::copyStructure(PVStructurePtr const & from, PVStructurePtr const &
 {
     if(to->isImmutable()) {
         if(from==to) return;
-        String message("Convert.copyStructure destination is immutable");
-        throw std::invalid_argument(message);
+        throw std::invalid_argument("Convert.copyStructure destination is immutable");
     }
     if(from==to) return;
     PVFieldPtrArray const & fromDatas = from->getPVFields();
@@ -343,6 +339,10 @@ void Convert::copyStructure(PVStructurePtr const & from, PVStructurePtr const &
             String message("Convert.copyStructure Illegal copyStructure");
             throw std::invalid_argument(message);
         }
+        if(toData->isImmutable()) {
+            if(fromData==toData) return;
+            throw std::invalid_argument("Convert.copyStructure destination is immutable");
+        }
         switch(fromType) {
         case scalar:
             {
@@ -415,8 +415,4 @@ ConvertPtr Convert::getConvert()
     return convert;
 }
 
-ConvertPtr getConvert() {
-    return Convert::getConvert();
-}
-
 }}
diff --git a/pvDataApp/pv/convert.h b/pvDataApp/pv/convert.h
index 4afa9e5..1aa5e71 100644
--- a/pvDataApp/pv/convert.h
+++ b/pvDataApp/pv/convert.h
@@ -89,7 +89,7 @@ public:
      * @param  Second field
      * @return (false, true) if the fields (are not, are) the same.
      */
-    bool equals(PVFieldPtr const &a,PVFieldPtr const &b)
+    inline bool equals(PVFieldPtr const &a,PVFieldPtr const &b)
     {
         return *a==*b;
     }
@@ -101,7 +101,7 @@ public:
      * @param  Second field
      * @return (false, true) if the fields (are not, are) the same.
      */
-    bool equals(PVField &a,PVField &b)
+    inline bool equals(PVField &a,PVField &b)
     {
         return a==b;
     }
@@ -820,12 +820,9 @@ public:
 private:
     Convert();
     PVDataCreatePtr pvDataCreate;
-    String trueString;
-    String falseString;
-    String illegalScalarType;
 };
 
-extern ConvertPtr getConvert();
+static inline ConvertPtr getConvert() { return Convert::getConvert(); }
     
 }}
 #endif  /* CONVERT_H */
diff --git a/pvDataApp/pv/pvData.h b/pvDataApp/pv/pvData.h
index 3ef001c..164406f 100644
--- a/pvDataApp/pv/pvData.h
+++ b/pvDataApp/pv/pvData.h
@@ -501,6 +501,10 @@ protected:
     }
     virtual void assign(const PVScalar& scalar)
     {
+        if(this==&scalar)
+            return;
+        if(isImmutable())
+            throw std::invalid_argument("Destination is immutable");
         T result;
         scalar.getAs((void*)&result, typeCode);
         put(result);