diff --git a/src/caseconv.cpp b/src/caseconv.cpp
index b0a6f8d..8738d6b 100644
--- a/src/caseconv.cpp
+++ b/src/caseconv.cpp
@@ -435,7 +435,7 @@ bool isAllUpperUTF8(const char * s)
     return isAllUpper(s,0);
     }
 
-bool (*IsAllUpper)(const char * s) = NULL;
+bool (*IsAllUpper)(const char * s) = 0;
 
 
 void AllToLowerISO(char * s)
diff --git a/src/text.h b/src/text.h
index 9e94cf3..b935ed3 100644
--- a/src/text.h
+++ b/src/text.h
@@ -94,7 +94,7 @@ class text
         bool InputHasTags;
         bool StartOfLine;
     private:
-        virtual const char* convert(const char* s, char* buf, const char* lastBufByte) = NULL;
+        virtual const char* convert(const char* s, char* buf, const char* lastBufByte) = 0;
             /*{
             REFER(buf)
             REFER(lastBufByte)
@@ -153,7 +153,7 @@ class text
             FILE* fpi
 #endif
             , optionStruct& Option
-        ) = NULL;
+        ) = 0;
         virtual ~text();
         void createUnTaggedAlternatives(
 #ifndef CONSTSTRCHR