diff --git a/zconf.h b/zconf.h
index b0c368c839..c15ff62771 100644
--- a/zconf.h
+++ b/zconf.h
@@ -511,7 +511,7 @@ typedef uLong FAR uLongf;
 
 #if !defined(_WIN32) && defined(Z_LARGE64)
 #  define z_off64_t off64_t
-#elif defined(_WIN32) || (defined(__GNUC__) && defined(__int64))
+#elif (defined(_WIN32) && !defined(__GNUC__)) || (defined(__GNUC__) && defined(__int64))
 #  define z_off64_t __int64
 #elif defined(__GO32__)
 #  define z_off64_t offset_t
diff --git a/zconf.h.cmakein b/zconf.h.cmakein
index 427b649451..4407982de5 100644
--- a/zconf.h.cmakein
+++ b/zconf.h.cmakein
@@ -513,7 +513,7 @@ typedef uLong FAR uLongf;
 
 #if !defined(_WIN32) && defined(Z_LARGE64)
 #  define z_off64_t off64_t
-#elif defined(_WIN32) || (defined(__GNUC__) && defined(__int64))
+#elif (defined(_WIN32) && !defined(__GNUC__)) || (defined(__GNUC__) && defined(__int64))
 #  define z_off64_t __int64
 #elif defined(__GO32__)
 #  define z_off64_t offset_t
diff --git a/zconf.h.in b/zconf.h.in
index b0c368c839..c15ff62771 100644
--- a/zconf.h.in
+++ b/zconf.h.in
@@ -511,7 +511,7 @@ typedef uLong FAR uLongf;
 
 #if !defined(_WIN32) && defined(Z_LARGE64)
 #  define z_off64_t off64_t
-#elif defined(_WIN32) || (defined(__GNUC__) && defined(__int64))
+#elif (defined(_WIN32) && !defined(__GNUC__)) || (defined(__GNUC__) && defined(__int64))
 #  define z_off64_t __int64
 #elif defined(__GO32__)
 #  define z_off64_t offset_t