diff --git a/src/AsynDriverInterface.cc b/src/AsynDriverInterface.cc
index 861957c..546a548 100644
--- a/src/AsynDriverInterface.cc
+++ b/src/AsynDriverInterface.cc
@@ -162,7 +162,7 @@ class AsynDriverInterface : StreamBusInterface
     double writeTimeout;
     double readTimeout;
     double replyTimeout;
-    size_t expectedLength;
+    ssize_t expectedLength;
     unsigned long eventMask;
     unsigned long receivedEvent;
     StreamBuffer inputBuffer;
@@ -187,7 +187,7 @@ class AsynDriverInterface : StreamBusInterface
     bool writeRequest(const void* output, size_t size,
         unsigned long writeTimeout_ms);
     bool readRequest(unsigned long replyTimeout_ms,
-        unsigned long readTimeout_ms, size_t expectedLength, bool async);
+        unsigned long readTimeout_ms, ssize_t expectedLength, bool async);
     bool acceptEvent(unsigned long mask, unsigned long replytimeout_ms);
     bool supportsEvent();
     bool supportsAsyncRead();
@@ -800,7 +800,7 @@ writeHandler()
 // interface function: we want to read something
 bool AsynDriverInterface::
 readRequest(unsigned long replyTimeout_ms, unsigned long readTimeout_ms,
-    size_t _expectedLength, bool async)
+    ssize_t _expectedLength, bool async)
 {
     debug("AsynDriverInterface::readRequest(%s, %ld msec reply, "
         "%ld msec read, expect %" Z "u bytes, async=%s)\n",
diff --git a/src/ChecksumConverter.cc b/src/ChecksumConverter.cc
index 0317617..731a607 100644
--- a/src/ChecksumConverter.cc
+++ b/src/ChecksumConverter.cc
@@ -706,13 +706,14 @@ scanPseudo(const StreamFormat& format, StreamBuffer& input, size_t& cursor)
     debug("ChecksumConverter %s: input to check: \"%s\n",
         checksumMap[fnum].name, input.expand(start,length)());
 
-    uint_fast8_t expectedLength =
+    uint_fast8_t nDigits =
         // get number of decimal digits from number of bytes: ceil(bytes*2.5)
         format.flags & sign_flag ? (checksumMap[fnum].bytes + 1) * 25 / 10 - 2 :
         format.flags & (zero_flag|left_flag) ? 2 * checksumMap[fnum].bytes :
         checksumMap[fnum].bytes;
+    ssize_t expectedLength = nDigits;
 
-    if (input.length() - cursor < expectedLength)
+    if ((ssize_t)( input.length() - cursor ) < expectedLength)
     {
         debug("ChecksumConverter %s: Input '%s' too short for checksum\n",
             checksumMap[fnum].name, input.expand(cursor)());
@@ -731,7 +732,7 @@ scanPseudo(const StreamFormat& format, StreamBuffer& input, size_t& cursor)
     if (format.flags & sign_flag) // decimal
     {
         uint32_t sumin = 0;
-        size_t i;
+        ssize_t i;
         for (i = 0; i < expectedLength; i++)
         {
             inchar = input[cursor+i];
@@ -753,7 +754,7 @@ scanPseudo(const StreamFormat& format, StreamBuffer& input, size_t& cursor)
         {
             if (format.flags & zero_flag) // ASCII
             {
-                if (sscanf(input(cursor+2*i), "%2" SCNx8, &inchar) != 1)
+                if (sscanf(input(cursor+2*i), "%2" SCNx8, (int8_t *) &inchar) != 1)
                 {
                     debug("ChecksumConverter %s: Input byte '%s' is not a hex byte\n",
                         checksumMap[fnum].name, input.expand(cursor+2*i,2)());
@@ -797,7 +798,7 @@ scanPseudo(const StreamFormat& format, StreamBuffer& input, size_t& cursor)
         {
             if (format.flags & zero_flag) // ASCII
             {
-                sscanf(input(cursor+2*i), "%2" SCNx8, &inchar);
+                sscanf(input(cursor+2*i), "%2" SCNx8, (int8_t *) &inchar);
             }
             else
             if (format.flags & left_flag) // poor man's hex: 0x30 - 0x3F
diff --git a/src/DebugInterface.cc b/src/DebugInterface.cc
index 89c5dbb..3d3e527 100644
--- a/src/DebugInterface.cc
+++ b/src/DebugInterface.cc
@@ -37,7 +37,7 @@ class DebugInterface : StreamBusInterface
     bool writeRequest(const void* output, size_t size,
         unsigned long writeTimeout_ms);
     bool readRequest(unsigned long replyTimeout_ms,
-        unsigned long readTimeout_ms, size_t expectedLength, bool async);
+        unsigned long readTimeout_ms, ssize_t expectedLength, bool async);
 
 protected:
     ~DebugInterface();
@@ -169,9 +169,9 @@ writeRequest(const void* output, size_t size, unsigned long writeTimeout_ms)
 // Return false if the read request cannot be accepted.
 bool DebugInterface::
 readRequest(unsigned long replyTimeout_ms, unsigned long readTimeout_ms,
-    size_t expectedLength, bool async)
+    ssize_t expectedLength, bool async)
 {
-    debug("DebugInterface::readRequest(%s, %ld msec reply, %ld msec read, expect %" Z "u bytes, asyn=%s)\n",
+    debug("DebugInterface::readRequest(%s, %ld msec reply, %ld msec read, expect %" Z "d bytes, asyn=%s)\n",
         clientName(), replyTimeout_ms, readTimeout_ms, expectedLength, async?"yes":"no");
 
     // Debug interface does not support async mode.
diff --git a/src/StreamBusInterface.cc b/src/StreamBusInterface.cc
index 41517dd..9edc4af 100644
--- a/src/StreamBusInterface.cc
+++ b/src/StreamBusInterface.cc
@@ -118,7 +118,7 @@ writeRequest(const void*, size_t, unsigned long)
 }
 
 bool StreamBusInterface::
-readRequest(unsigned long, unsigned long, size_t, bool)
+readRequest(unsigned long, unsigned long, ssize_t, bool)
 {
     return false;
 }
diff --git a/src/StreamBusInterface.h b/src/StreamBusInterface.h
index b734c25..7ca163e 100644
--- a/src/StreamBusInterface.h
+++ b/src/StreamBusInterface.h
@@ -76,7 +76,7 @@ public:
             return businterface && businterface->writeRequest(output, size, timeout_ms);
         }
         bool busReadRequest(unsigned long replytimeout_ms,
-            unsigned long readtimeout_ms, size_t expectedLength,
+            unsigned long readtimeout_ms, ssize_t expectedLength,
             bool async) {
             return businterface && businterface->readRequest(replytimeout_ms,
                     readtimeout_ms, expectedLength, async);
@@ -133,7 +133,7 @@ protected:
     virtual bool writeRequest(const void* output, size_t size,
         unsigned long timeout_ms);
     virtual bool readRequest(unsigned long replytimeout_ms,
-        unsigned long readtimeout_ms, size_t expectedLength,
+        unsigned long readtimeout_ms, ssize_t expectedLength,
         bool async);
     virtual bool supportsEvent(); // defaults to false
     virtual bool supportsAsyncRead(); // defaults to false