diff --git a/src-input/duk_numconv.c b/src-input/duk_numconv.c
index f2a312e1c4..03dcdf9c6e 100644
--- a/src-input/duk_numconv.c
+++ b/src-input/duk_numconv.c
@@ -88,7 +88,7 @@ typedef struct {
 #if defined(DUK_USE_DEBUG_LEVEL) && (DUK_USE_DEBUG_LEVEL >= 2)
 DUK_LOCAL void duk__bi_print(const char *name, duk__bigint *x) {
 	/* Overestimate required size; debug code so not critical to be tight. */
-	char buf[DUK__BI_MAX_PARTS * 9 + 64];
+	char buf[DUK__BI_MAX_PARTS * 9 + 64 + 1];
 	char *p = buf;
 	duk_small_int_t i;