diff --git a/Makefile b/Makefile
index ad713dd..73d99b5 100644
--- a/Makefile
+++ b/Makefile
@@ -4,7 +4,7 @@ PREFIX=/usr/local
 SYSCONFDIR=/etc
 CFLAGS=-std=c11 -Werror -D_XOPEN_SOURCE=700 -D_POSIX_C_SOURCE=200809L -fPIC -flto=auto -fvisibility=hidden \
 			 -fsanitize=signed-integer-overflow -fno-sanitize-recover
-CWARN=-Wall -Wextra -Wno-format
+CWARN=-Wall -Wextra -Wno-format -Wshadow
   # -Wpedantic -Wsign-conversion -Wtype-limits -Wunused-result -Wnull-dereference \
 	# -Waggregate-return -Walloc-zero -Walloca -Warith-conversion -Wcast-align -Wcast-align=strict \
 	# -Wdangling-else -Wdate-time -Wdisabled-optimization -Wdouble-promotion -Wduplicated-branches \
diff --git a/match.c b/match.c
index 6336479..9dbd789 100644
--- a/match.c
+++ b/match.c
@@ -97,7 +97,7 @@ static match_t *clone_match(match_t *m)
         for (int i = 0; m->children[i]; i++) {
             if (nchildren+1 >= child_cap) {
                 ret->children = grow(ret->children, child_cap += 5);
-                for (size_t i = nchildren; i < child_cap; i++) ret->children[i] = NULL;
+                for (size_t j = nchildren; j < child_cap; j++) ret->children[j] = NULL;
             }
             ret->children[nchildren++] = clone_match(m->children[i]);
         }