diff --git a/lib/libc/string/ffs.c b/lib/libc/string/ffs.c
--- a/lib/libc/string/ffs.c
+++ b/lib/libc/string/ffs.c
@@ -47,5 +47,9 @@
 int
 ffs(int mask)
 {
+#ifdef __clang__
 	return (__builtin_ffs(mask));
+#else /* gcc */
+	return (mask == 0 ? 0 : __builtin_ctz(mask) + 1);
+#endif
 }
diff --git a/lib/libc/string/ffsl.c b/lib/libc/string/ffsl.c
--- a/lib/libc/string/ffsl.c
+++ b/lib/libc/string/ffsl.c
@@ -44,5 +44,9 @@
 int
 ffsl(long mask)
 {
+#ifdef __clang__
 	return (__builtin_ffsl(mask));
+#else /* gcc */
+	return (mask == 0 ? 0 : __builtin_ctzl(mask) + 1);
+#endif
 }
diff --git a/lib/libc/string/ffsll.c b/lib/libc/string/ffsll.c
--- a/lib/libc/string/ffsll.c
+++ b/lib/libc/string/ffsll.c
@@ -44,5 +44,9 @@
 int
 ffsll(long long mask)
 {
+#ifdef __clang__
 	return (__builtin_ffsll(mask));
+#else /* gcc */
+	return (mask == 0 ? 0 : __builtin_ctzll(mask) + 1);
+#endif
 }
diff --git a/tools/build/depend-cleanup.sh b/tools/build/depend-cleanup.sh
--- a/tools/build/depend-cleanup.sh
+++ b/tools/build/depend-cleanup.sh
@@ -124,3 +124,11 @@
 	    "$OBJTOP"/obj-lib32/secure/lib/libcrypto \
 	    "$OBJTOP"/obj-lib32/secure/lib/libssl
 fi
+
+# 20230707  ee8b0c436d72    ffs/fls replaced
+clean_dep   lib/libc        ffs   S
+clean_dep   lib/libc        ffsl  S
+clean_dep   lib/libc        ffsll S
+clean_dep   lib/libc        fls   S
+clean_dep   lib/libc        flsl  S
+clean_dep   lib/libc        flsll S