diff --git a/deps/jemalloc/src/malloc_io.c b/deps/jemalloc/src/malloc_io.c
index 7bdc13f95..dd8826511 100644
--- a/deps/jemalloc/src/malloc_io.c
+++ b/deps/jemalloc/src/malloc_io.c
@@ -362,7 +362,7 @@ malloc_vsnprintf(char *str, size_t size, const char *format, va_list ap) {
 	}								\
 } while (0)
 #define GET_ARG_NUMERIC(val, len) do {					\
-	switch (len) {							\
+	switch ((unsigned char)len) {					\
 	case '?':							\
 		val = va_arg(ap, int);					\
 		break;							\