diff --git a/UPGRADING.INTERNALS b/UPGRADING.INTERNALS
index 1e8de617332..e5dc067fe88 100644
--- a/UPGRADING.INTERNALS
+++ b/UPGRADING.INTERNALS
@@ -6,6 +6,7 @@ PHP 8.1 INTERNALS UPGRADE NOTES
   c. zend_get_opcode_id()
 
 2. Build system changes
+  a. New compiler flags
 
 3. Module changes
   a. ext/hash
@@ -39,7 +40,9 @@ PHP 8.1 INTERNALS UPGRADE NOTES
 ========================
 2. Build system changes
 ========================
-
+  a. New compiler flags
+     - [-Wimplicit-fallthrough=1] is now enabled by default.
+       It is possible to use the new ZEND_FALLTHROUGH macro keyword to suppress the warning.
 ========================
 3. Module changes
 ========================
diff --git a/Zend/Zend.m4 b/Zend/Zend.m4
index a2e506412db..bbfc3985a7b 100644
--- a/Zend/Zend.m4
+++ b/Zend/Zend.m4
@@ -206,9 +206,11 @@ else
   AC_DEFINE(ZEND_DEBUG,0,[ ])
 fi
 
-test -n "$GCC" && CFLAGS="-Wall -Wextra -Wno-strict-aliasing -Wno-implicit-fallthrough -Wno-unused-parameter -Wno-sign-compare $CFLAGS"
+test -n "$GCC" && CFLAGS="-Wall -Wextra -Wno-strict-aliasing -Wno-unused-parameter -Wno-sign-compare $CFLAGS"
 dnl Check if compiler supports -Wno-clobbered (only GCC)
 AX_CHECK_COMPILE_FLAG([-Wno-clobbered], CFLAGS="-Wno-clobbered $CFLAGS", , [-Werror])
+dnl Check for support for implicit fallthrough level 1, also add after previous CFLAGS as level 3 is enabled in -Wextra
+AX_CHECK_COMPILE_FLAG([-Wimplicit-fallthrough=1], CFLAGS="$CFLAGS -Wimplicit-fallthrough=1", , [-Werror])
 AX_CHECK_COMPILE_FLAG([-Wduplicated-cond], CFLAGS="-Wduplicated-cond $CFLAGS", , [-Werror])
 AX_CHECK_COMPILE_FLAG([-Wlogical-op], CFLAGS="-Wlogical-op $CFLAGS", , [-Werror])
 AX_CHECK_COMPILE_FLAG([-Wformat-truncation], CFLAGS="-Wformat-truncation $CFLAGS", , [-Werror])
diff --git a/ext/date/config0.m4 b/ext/date/config0.m4
index 20cf546c7e3..18b8106bd2d 100644
--- a/ext/date/config0.m4
+++ b/ext/date/config0.m4
@@ -4,7 +4,7 @@ AC_CHECK_HEADERS([io.h])
 dnl Check for strtoll, atoll
 AC_CHECK_FUNCS(strtoll atoll)
 
-PHP_DATE_CFLAGS="-I@ext_builddir@/lib -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1 -DHAVE_TIMELIB_CONFIG_H=1"
+PHP_DATE_CFLAGS="-Wno-implicit-fallthrough -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 0dbb081b6c7..4b9abf939ad 100644
--- a/ext/hash/config.m4
+++ b/ext/hash/config.m4
@@ -28,7 +28,8 @@ else
     SHA3_OPT_SRC="$SHA3_DIR/KeccakP-1600-opt64.c"
   ])
   EXT_HASH_SHA3_SOURCES="$SHA3_OPT_SRC $SHA3_DIR/KeccakHash.c $SHA3_DIR/KeccakSponge.c hash_sha3.c"
-  PHP_HASH_CFLAGS="-I@ext_srcdir@/$SHA3_DIR -DKeccakP200_excluded -DKeccakP400_excluded -DKeccakP800_excluded -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1"
+  dnl Add -Wno-implicit-fallthrough flag as it happens on 32 bit builds
+  PHP_HASH_CFLAGS="-Wno-implicit-fallthrough -I@ext_srcdir@/$SHA3_DIR -DKeccakP200_excluded -DKeccakP400_excluded -DKeccakP800_excluded -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1"
 
   PHP_ADD_BUILD_DIR(ext/hash/$SHA3_DIR, 1)
 fi
diff --git a/ext/opcache/config.m4 b/ext/opcache/config.m4
index 2002eaa9b64..27882c6a764 100644
--- a/ext/opcache/config.m4
+++ b/ext/opcache/config.m4
@@ -326,7 +326,7 @@ int main() {
 	shared_alloc_mmap.c \
 	shared_alloc_posix.c \
 	$ZEND_JIT_SRC,
-	shared,,-DZEND_ENABLE_STATIC_TSRMLS_CACHE=1,,yes)
+	shared,,"-Wno-implicit-fallthrough -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1",,yes)
 
   PHP_ADD_EXTENSION_DEP(opcache, pcre)