diff --git a/release/c/wuffs-unsupported-snapshot.c b/release/c/wuffs-unsupported-snapshot.c
index 2ef8dda..18a4465 100644
--- a/release/c/wuffs-unsupported-snapshot.c
+++ b/release/c/wuffs-unsupported-snapshot.c
@@ -36900,7 +36900,7 @@
       }
       v_a32 = t_0;
     }
-    if (v_a32 >= 2147483648) {
+    if ((v_a32 == 0) || (v_a32 >= 2147483648)) {
       status = wuffs_base__make_status(wuffs_png__error__bad_header);
       goto exit;
     } else if (v_a32 >= 16777216) {
@@ -36937,7 +36937,7 @@
       }
       v_a32 = t_1;
     }
-    if (v_a32 >= 2147483648) {
+    if ((v_a32 == 0) || (v_a32 >= 2147483648)) {
       status = wuffs_base__make_status(wuffs_png__error__bad_header);
       goto exit;
     } else if (v_a32 >= 16777216) {
diff --git a/std/png/decode_png.wuffs b/std/png/decode_png.wuffs
index 0ab771d..41680d1 100644
--- a/std/png/decode_png.wuffs
+++ b/std/png/decode_png.wuffs
@@ -219,7 +219,7 @@
 	var a8  : base.u8
 
 	a32 = args.src.read_u32be?()
-	if a32 >= 0x8000_0000 {
+	if (a32 == 0) or (a32 >= 0x8000_0000) {
 		return "#bad header"
 	} else if a32 >= 0x0100_0000 {
 		return "#unsupported PNG file"
@@ -227,7 +227,7 @@
 	this.width = a32
 
 	a32 = args.src.read_u32be?()
-	if a32 >= 0x8000_0000 {
+	if (a32 == 0) or (a32 >= 0x8000_0000) {
 		return "#bad header"
 	} else if a32 >= 0x0100_0000 {
 		return "#unsupported PNG file"