diff --git a/include/git2/common.h b/include/git2/common.h
index a004be99b..ef279eac1 100644
--- a/include/git2/common.h
+++ b/include/git2/common.h
@@ -64,7 +64,7 @@
 # define GIT_FORMAT_PRINTF(a,b) /* empty */
 #endif
 
-#if defined(_WIN32) && !defined(__CYGWIN__)
+#if (defined(_WIN32) || defined(_WIN64)) && !defined(__CYGWIN__)
 #define GIT_WIN32 1
 #endif