diff --git a/Python/pystrtod.c b/Python/pystrtod.c
index 16dac81ff61..909e0210ea2 100644
--- a/Python/pystrtod.c
+++ b/Python/pystrtod.c
@@ -1005,6 +1005,7 @@ format_float_short(double d, char format_code,
 			/* shouldn't get here: Gay's code should always return
 			   something starting with a digit, an 'I',  or 'N' */
 			strncpy(p, "ERR", 3);
+			p += 3;
 			assert(0);
 		}
 		goto exit;