diff --git a/Modules/regexpr.c b/Modules/regexpr.c
index 8b36580..8694c74 100644
--- a/Modules/regexpr.c
+++ b/Modules/regexpr.c
@@ -1383,7 +1383,7 @@
 			if (a < '0' || a > '9')
 				goto bad_match_register;
 			ch = 10 * (a - '0') + ch - '0';
-			if (ch <= 0 || ch >= RE_NREGS)
+			if (ch == 0 || ch >= RE_NREGS)
 				goto bad_match_register;
 			bufp->uses_registers = 1;
 			opcode = Cmatch_memory;