diff --git a/ext/date/config0.m4 b/ext/date/config0.m4
index 8aee3bc7185..551291e2505 100644
--- a/ext/date/config0.m4
+++ b/ext/date/config0.m4
@@ -4,7 +4,11 @@ AC_CHECK_HEADERS([io.h])
 dnl Check for strtoll, atoll
 AC_CHECK_FUNCS([strtoll atoll])
 
-PHP_DATE_CFLAGS="-Wno-implicit-fallthrough -I@ext_builddir@/lib -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1 -DHAVE_TIMELIB_CONFIG_H=1"
+AX_CHECK_COMPILE_FLAG([-Wno-implicit-fallthrough],
+  [PHP_DATE_CFLAGS="$PHP_DATE_CFLAGS -Wno-implicit-fallthrough"],,
+  [-Werror])
+
+PHP_DATE_CFLAGS="$PHP_DATE_CFLAGS -I@ext_builddir@/lib -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1 -DHAVE_TIMELIB_CONFIG_H=1"
 timelib_sources="lib/astro.c lib/dow.c lib/parse_date.c lib/parse_tz.c lib/parse_posix.c
                  lib/timelib.c lib/tm2unixtime.c lib/unixtime2tm.c lib/parse_iso_intervals.c lib/interval.c"
 
diff --git a/ext/hash/config.m4 b/ext/hash/config.m4
index af54e360aa6..363af5615d6 100644
--- a/ext/hash/config.m4
+++ b/ext/hash/config.m4
@@ -20,7 +20,9 @@ else
     SHA3_DIR="sha3/generic32lc"
     SHA3_OPT_SRC="$SHA3_DIR/KeccakP-1600-inplace32BI.c"
     dnl Add -Wno-implicit-fallthrough flag as it happens on 32 bit builds
-    PHP_HASH_CFLAGS="-Wno-implicit-fallthrough"
+    AX_CHECK_COMPILE_FLAG([-Wno-implicit-fallthrough],
+      [PHP_HASH_CFLAGS="$PHP_HASH_CFLAGS -Wno-implicit-fallthrough"],,
+      [-Werror])
   ],[
     AC_MSG_RESULT([yes])
     SHA3_DIR="sha3/generic64lc"
diff --git a/ext/pcre/config0.m4 b/ext/pcre/config0.m4
index 0395cd631e3..6d95d78c07f 100644
--- a/ext/pcre/config0.m4
+++ b/ext/pcre/config0.m4
@@ -57,7 +57,12 @@ else
   pcre2lib/pcre2_string_utils.c pcre2lib/pcre2_study.c pcre2lib/pcre2_substitute.c  pcre2lib/pcre2_substring.c \
   pcre2lib/pcre2_tables.c pcre2lib/pcre2_ucd.c pcre2lib/pcre2_valid_utf.c pcre2lib/pcre2_xclass.c \
   pcre2lib/pcre2_find_bracket.c pcre2lib/pcre2_convert.c pcre2lib/pcre2_extuni.c pcre2lib/pcre2_script_run.c"
-  PHP_PCRE_CFLAGS="-Wno-implicit-fallthrough -DHAVE_CONFIG_H -DHAVE_MEMMOVE -I@ext_srcdir@/pcre2lib -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1"
+
+  AX_CHECK_COMPILE_FLAG([-Wno-implicit-fallthrough],
+    [PHP_PCRE_CFLAGS="$PHP_PCRE_CFLAGS -Wno-implicit-fallthrough"],,
+    [-Werror])
+
+  PHP_PCRE_CFLAGS="$PHP_PCRE_CFLAGS -DHAVE_CONFIG_H -I@ext_srcdir@/pcre2lib -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1"
   AC_DEFINE(HAVE_BUNDLED_PCRE, 1, [ ])
   AC_DEFINE(PCRE2_CODE_UNIT_WIDTH, 8, [ ])