diff --git a/stb_sprintf.h b/stb_sprintf.h
index 4335a30..841dfd6 100644
--- a/stb_sprintf.h
+++ b/stb_sprintf.h
@@ -15,6 +15,7 @@
 //    Rohit Nirmal
 //    Marcin Wojdyr
 //    Leonard Ritter
+//    Stefano Zanotti
 //
 // LICENSE:
 //
@@ -159,6 +160,7 @@ PERFORMANCE vs MSVC 2008 32-/64-bit (GCC is even slower than MSVC):
 #endif
 
 #include <stdarg.h> // for va_list()
+#include <stddef.h> // size_t, ptrdiff_t
 
 #ifndef STB_SPRINTF_MIN
 #define STB_SPRINTF_MIN 512 // how many characters per callback
@@ -457,13 +459,16 @@ STBSP__PUBLICDEF int STB_SPRINTF_DECORATE(vsprintfcb)(STBSP_SPRINTFCB *callback,
          break;
       // are we 64-bit on intmax? (c99)
       case 'j':
-         fl |= STBSP__INTMAX;
+         fl |= (sizeof(size_t) == 8) ? STBSP__INTMAX : 0;
          ++f;
          break;
       // are we 64-bit on size_t or ptrdiff_t? (c99)
       case 'z':
+         fl |= (sizeof(ptrdiff_t) == 8) ? STBSP__INTMAX : 0;
+         ++f;
+         break;
       case 't':
-         fl |= ((sizeof(char *) == 8) ? STBSP__INTMAX : 0);
+         fl |= (sizeof(ptrdiff_t) == 8) ? STBSP__INTMAX : 0;
          ++f;
          break;
       // are we 64-bit (msft style)