diff --git a/pngrutil.c b/pngrutil.c
index aad1cc42a..81195578e 100644
--- a/pngrutil.c
+++ b/pngrutil.c
@@ -22,14 +22,23 @@
    /* Check if zlib's inflateValidate can be used. */
 #  if ZLIB_VERNUM >= 0x1290 && \
      defined(PNG_SET_OPTION_SUPPORTED) && defined(PNG_IGNORE_ADLER32)
-      /* Determine at compile-time whether inflateValidate is available by
-       * minimal supported OS version.
-       */
-#     if defined(MAC_OS_X_VERSION_MIN_REQUIRED) && \
-        MAC_OS_X_VERSION_MIN_REQUIRED < 101300
-         /* Don't use if targeting pre-macOS 10.13. */
-#        define PNG_USE_ZLIB_INFLATE_VALIDATE 0
-#     endif
+#     if defined(__APPLE__) && defined(__MACH__)
+         /* Determine at compile-time whether inflateValidate is available by
+          * minimal supported OS version.
+          */
+
+         /* For MAC_OS_X_VERSION_MIN_REQUIRED.
+          * Not using the preferred <Availability.h> because it was introduced
+          * during the 10.5 SDK while this header has been available with Xcode
+          * since 1.0 (10.3 SDK).
+          */
+#        include <AvailabilityMacros.h>
+#        if defined(MAC_OS_X_VERSION_MIN_REQUIRED) && \
+           MAC_OS_X_VERSION_MIN_REQUIRED < 101300
+            /* Don't use if targeting pre-macOS 10.13. */
+#           define PNG_USE_ZLIB_INFLATE_VALIDATE 0
+#        endif
+#     endif /* __APPLE__ && __MACH__ */
 #  else
 #     define PNG_USE_ZLIB_INFLATE_VALIDATE 0
 #  endif /* ZLIB_VERNUM && PNG_SET_OPTION_SUPPORTED && PNG_IGNORE_ADLER32 */