diff --git a/Makefile.am b/Makefile.am
index faf236d1413f3..2de08840fefe0 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -738,6 +738,7 @@ php_EXTRA_DIST=                                                       \
   php/tests/autoload.php                                              \
   php/tests/bootstrap_phpunit.php                                     \
   php/tests/compatibility_test.sh                                     \
+  php/tests/compile_extension.sh                                      \
   php/tests/descriptors_test.php                                      \
   php/tests/encode_decode_test.php                                    \
   php/tests/gdb_test.sh                                               \
diff --git a/php/ext/google/protobuf/def.c b/php/ext/google/protobuf/def.c
index ef0f711672ff4..184ae2d36652e 100644
--- a/php/ext/google/protobuf/def.c
+++ b/php/ext/google/protobuf/def.c
@@ -853,9 +853,10 @@ static zend_class_entry *register_class(const upb_filedef *file,
 
   fill_namespace(package, php_namespace, &namesink);
   fill_classname(fullname, package, prefix, &namesink, use_nested_submsg);
+  stringsink_string(&namesink, NULL, "\0", 1, NULL);
 
   PHP_PROTO_CE_DECLARE pce;
-  if (php_proto_zend_lookup_class(namesink.ptr, namesink.len, &pce) ==
+  if (php_proto_zend_lookup_class(namesink.ptr, namesink.len - 1, &pce) ==
       FAILURE) {
     zend_error(
         E_ERROR,
diff --git a/php/tests/compile_extension.sh b/php/tests/compile_extension.sh
new file mode 100755
index 0000000000000..bbd669684c8eb
--- /dev/null
+++ b/php/tests/compile_extension.sh
@@ -0,0 +1,10 @@
+#!/bin/bash
+
+EXTENSION_PATH=$1
+
+pushd $EXTENSION_PATH
+make clean || true
+set -e
+# Add following in configure for debug: --enable-debug CFLAGS='-g -O0'
+phpize && ./configure CFLAGS='-g -O0' && make
+popd
diff --git a/php/tests/php_implementation_test.php b/php/tests/php_implementation_test.php
index 8d27d19f0db93..307b749c4930b 100644
--- a/php/tests/php_implementation_test.php
+++ b/php/tests/php_implementation_test.php
@@ -14,8 +14,19 @@
 use Google\Protobuf\Internal\GPBWire;
 use Google\Protobuf\Internal\CodedOutputStream;
 
+/**
+ * Please note, this test is only intended to be run without the protobuf C
+ * extension.
+ */
 class ImplementationTest extends TestBase
 {
+    public function setUp()
+    {
+        if (extension_loaded('protobuf')) {
+            $this->markTestSkipped();
+        }
+    }
+
     public function testReadInt32()
     {
         $value = null;
diff --git a/php/tests/test.sh b/php/tests/test.sh
index b5e8769e5ef54..be6e97fe8594d 100755
--- a/php/tests/test.sh
+++ b/php/tests/test.sh
@@ -7,12 +7,7 @@ export C_INCLUDE_PATH=/usr/local/php-$VERSION/include/php/main:/usr/local/php-$V
 export CPLUS_INCLUDE_PATH=/usr/local/php-$VERSION/include/php/main:/usr/local/php-$VERSION/include/php:$CPLUS_INCLUDE_PATH
 
 # Compile c extension
-pushd ../ext/google/protobuf/
-make clean || true
-set -e
-# Add following in configure for debug: --enable-debug CFLAGS='-g -O0'
-phpize && ./configure CFLAGS='-g -O0' && make
-popd
+/bin/bash ./compile_extension.sh ../ext/google/protobuf
 
 tests=( array_test.php encode_decode_test.php generated_class_test.php map_field_test.php well_known_test.php descriptors_test.php wrapper_type_setters_test.php)
 
diff --git a/tests.sh b/tests.sh
index 09edfbfb15a8a..265a8c0933390 100755
--- a/tests.sh
+++ b/tests.sh
@@ -467,6 +467,16 @@ build_php5.5_c() {
   # popd
 }
 
+build_php5.5_mixed() {
+  use_php 5.5
+  pushd php
+  rm -rf vendor
+  composer update
+  /bin/bash ./tests/compile_extension.sh ./ext/google/protobuf
+  php -dextension=./ext/google/protobuf/modules/protobuf.so ./vendor/bin/phpunit
+  popd
+}
+
 build_php5.5_zts_c() {
   use_php_zts 5.5
   cd php/tests && /bin/bash ./test.sh 5.5-zts && cd ../..
@@ -497,6 +507,16 @@ build_php5.6_c() {
   # popd
 }
 
+build_php5.6_mixed() {
+  use_php 5.6
+  pushd php
+  rm -rf vendor
+  composer update
+  /bin/bash ./tests/compile_extension.sh ./ext/google/protobuf
+  php -dextension=./ext/google/protobuf/modules/protobuf.so ./vendor/bin/phpunit
+  popd
+}
+
 build_php5.6_zts_c() {
   use_php_zts 5.6
   cd php/tests && /bin/bash ./test.sh 5.6-zts && cd ../..
@@ -552,6 +572,16 @@ build_php7.0_c() {
   # popd
 }
 
+build_php7.0_mixed() {
+  use_php 7.0
+  pushd php
+  rm -rf vendor
+  composer update
+  /bin/bash ./tests/compile_extension.sh ./ext/google/protobuf
+  php -dextension=./ext/google/protobuf/modules/protobuf.so ./vendor/bin/phpunit
+  popd
+}
+
 build_php7.0_zts_c() {
   use_php_zts 7.0
   cd php/tests && /bin/bash ./test.sh 7.0-zts && cd ../..
@@ -615,6 +645,16 @@ build_php7.1_c() {
   fi
 }
 
+build_php7.1_mixed() {
+  use_php 7.1
+  pushd php
+  rm -rf vendor
+  composer update
+  /bin/bash ./tests/compile_extension.sh ./ext/google/protobuf
+  php -dextension=./ext/google/protobuf/modules/protobuf.so ./vendor/bin/phpunit
+  popd
+}
+
 build_php7.1_zts_c() {
   use_php_zts 7.1
   cd php/tests && /bin/bash ./test.sh 7.1-zts && cd ../..
@@ -632,6 +672,10 @@ build_php_all_32() {
   build_php5.6_c
   build_php7.0_c
   build_php7.1_c $1
+  build_php5.5_mixed
+  build_php5.6_mixed
+  build_php7.0_mixed
+  build_php7.1_mixed
   build_php5.5_zts_c
   build_php5.6_zts_c
   build_php7.0_zts_c