diff --git a/src/util/string.c b/src/util/string.c
index 4a9e35de5..7d1b92c59 100644
--- a/src/util/string.c
+++ b/src/util/string.c
@@ -124,11 +124,13 @@ static const uint8_t _utf8len[0x40] = {
 };
 
 uint32_t utf8Char(const char** unicode, size_t* length) {
-	if (*length == 0) {
+	if (length && *length == 0) {
 		return 0;
 	}
 	unsigned char byte = **unicode;
-	--*length;
+	if (length) {
+		--*length;
+	}
 	++*unicode;
 	if (!(byte & 0x80)) {
 		return byte;
@@ -140,7 +142,7 @@ uint32_t utf8Char(const char** unicode, size_t* length) {
 	if (numBytes == 0) {
 		return 0xFFFD;
 	}
-	if (*length + 1 < numBytes) {
+	if (length && *length + 1 < numBytes) {
 		*length = 0;
 		return 0xFFFD;
 	}
@@ -148,7 +150,9 @@ uint32_t utf8Char(const char** unicode, size_t* length) {
 	for (i = 1; i < numBytes; ++i) {
 		unichar <<= 6;
 		byte = **unicode;
-		--*length;
+		if (length) {
+			--*length;
+		}
 		++*unicode;
 		if ((byte & 0xC0) != 0x80) {
 			return 0;