diff --git a/pngpriv.h b/pngpriv.h
index 583c26f9b..d734f9746 100644
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -185,6 +185,8 @@
       /* Use the intrinsics code by default. */
 #     define PNG_ARM_NEON_IMPLEMENTATION 1
 #  endif
+#else /* PNG_ARM_NEON_OPT == 0 */
+#     define PNG_ARM_NEON_IMPLEMENTATION 0
 #endif /* PNG_ARM_NEON_OPT > 0 */
 
 #ifndef PNG_MIPS_MSA_OPT