diff --git a/dtool/src/dtoolbase/dtoolbase.h b/dtool/src/dtoolbase/dtoolbase.h
index f21e653695..2f8e7ca05d 100644
--- a/dtool/src/dtoolbase/dtoolbase.h
+++ b/dtool/src/dtoolbase/dtoolbase.h
@@ -63,8 +63,10 @@
 /* Windows likes to define min() and max() macros, which will conflict with
    std::min() and std::max() respectively, unless we do this: */
 #ifdef WIN32
+#ifndef NOMINMAX
 #define NOMINMAX
 #endif
+#endif
 
 #ifndef __has_builtin
 #define __has_builtin(x) 0