diff --git a/panda/src/pnm/Sources.pp b/panda/src/pnm/Sources.pp
index a0041386ea..b204623ad7 100644
--- a/panda/src/pnm/Sources.pp
+++ b/panda/src/pnm/Sources.pp
@@ -2,7 +2,10 @@
                    dtoolutil:c dtoolbase:c dtool:m
 #define LOCAL_LIBS pandabase
 
-#define CFLAGS /D__STDC__
+#if $[or $[eq $[USE_COMPILER],MSVC],$[eq $[USE_COMPILER],INTEL]]
+  #define CFLAGS /D__STDC__
+#endif
+
 #begin lib_target
   #define TARGET pnm