diff --git a/.bazelrc b/.bazelrc
index 65cc8c491e52..8ca6e56dd812 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -1,5 +1,8 @@
 build --cxxopt=-std=c++17 --host_cxxopt=-std=c++17
 
+build --copt="-Werror" --copt="-Wno-sign-compare" --copt="-Wno-sign-conversion" --copt="-Wno-error=sign-conversion"  --copt="-Wno-deprecated-declarations"
+
+
 build:dbg --compilation_mode=dbg
 
 build:opt --compilation_mode=opt
diff --git a/.github/workflows/test_objectivec.yml b/.github/workflows/test_objectivec.yml
index 1db6c10c88ab..ab3a5af4b37c 100644
--- a/.github/workflows/test_objectivec.yml
+++ b/.github/workflows/test_objectivec.yml
@@ -76,6 +76,7 @@ jobs:
           - OS: macos-14
             PLATFORM: "visionos"
             XCODE: "15.2"
+            EXTRA_FLAGS: --copt="-Wno-deprecated-non-prototype"
     name: CocoaPods ${{ matrix.PLATFORM }} ${{ matrix.CONFIGURATION }}
     runs-on: ${{ matrix.OS }}
     steps:
@@ -91,7 +92,7 @@ jobs:
           credentials: ${{ secrets.GAR_SERVICE_ACCOUNT }}
           bazel-cache: cocoapods/${{ matrix.XCODE }}
           bash: |
-            ./regenerate_stale_files.sh $BAZEL_FLAGS --xcode_version="${{ matrix.XCODE }}"
+            ./regenerate_stale_files.sh $BAZEL_FLAGS ${{ matrix.EXTRA_FLAGS }} --xcode_version="${{ matrix.XCODE }}"
             pod lib lint --verbose \
               --configuration=${{ matrix.CONFIGURATION }} \
               --platforms=${{ matrix.PLATFORM }} \
diff --git a/.github/workflows/test_rust.yml b/.github/workflows/test_rust.yml
index 00c2e4b7bb45..2f7021c0b90a 100644
--- a/.github/workflows/test_rust.yml
+++ b/.github/workflows/test_rust.yml
@@ -27,6 +27,7 @@ jobs:
           credentials: ${{ secrets.GAR_SERVICE_ACCOUNT }}
           bazel-cache: rust_linux
           bazel: >-
-            test //rust:protobuf_upb_test //rust:protobuf_cpp_test
+            test --cxxopt=-std=c++17 --host_cxxopt=-std=c++17 --copt="-Wno-return-type-c-linkage"
+            //rust:protobuf_upb_test //rust:protobuf_cpp_test
             //rust/test/rust_proto_library_unit_test:rust_upb_aspect_test
             //src/google/protobuf/compiler/rust/...
diff --git a/.github/workflows/test_upb.yml b/.github/workflows/test_upb.yml
index 945b7c01b4f4..7490e75f754d 100644
--- a/.github/workflows/test_upb.yml
+++ b/.github/workflows/test_upb.yml
@@ -59,7 +59,10 @@ jobs:
           image: "us-docker.pkg.dev/protobuf-build/containers/test/linux/gcc:12.2-6.3.0-63dd26c0c7a808d92673a3e52e848189d4ab0f17"
           credentials: ${{ secrets.GAR_SERVICE_ACCOUNT }}
           bazel-cache: "upb-bazel-gcc"
-          bazel: test --cxxopt=-std=c++17 --host_cxxopt=-std=c++17 -c opt //bazel/... //benchmarks/... //lua/... //python/... //upb/... //upb_generator/...
+          bazel: >-
+            test --cxxopt=-std=c++17 --host_cxxopt=-std=c++17 -c opt
+            --copt="-Wno-error=maybe-uninitialized" --copt="-Wno-error=attributes"
+            //bazel/... //benchmarks/... //lua/... //python/... //upb/... //upb_generator/...
 
   windows:
     strategy:
diff --git a/build_defs/cpp_opts.bzl b/build_defs/cpp_opts.bzl
index 46b60252f62b..d8646d1681fe 100644
--- a/build_defs/cpp_opts.bzl
+++ b/build_defs/cpp_opts.bzl
@@ -21,7 +21,6 @@ COPTS = select({
         "-Woverloaded-virtual",
         "-Wno-sign-compare",
         "-Wno-nonnull",
-        "-Werror",
     ],
 })
 
diff --git a/ci/Linux.bazelrc b/ci/Linux.bazelrc
index d5dcf5de005d..b4ec98f8c796 100644
--- a/ci/Linux.bazelrc
+++ b/ci/Linux.bazelrc
@@ -1,3 +1,4 @@
 import common.bazelrc
 
 build --cxxopt=-std=c++14 --host_cxxopt=-std=c++14
+build --copt="-Werror" --copt="-Wno-sign-compare" --copt="-Wno-sign-conversion" --copt="-Wno-error=sign-conversion" --copt="-Wno-deprecated-declarations"
diff --git a/ci/macOS.bazelrc b/ci/macOS.bazelrc
index 8e7eaf0fb381..e1336ca1cd23 100644
--- a/ci/macOS.bazelrc
+++ b/ci/macOS.bazelrc
@@ -1,5 +1,6 @@
 import common.bazelrc
 
 build --cxxopt=-std=c++14 --host_cxxopt=-std=c++14
+build --copt="-Werror" --copt="-Wno-sign-compare" --copt="-Wno-sign-conversion" --copt="-Wno-error=sign-conversion" --copt="-Wno-deprecated-declarations"
 common --repo_env=BAZEL_NO_APPLE_CPP_TOOLCHAIN=1
-common --xcode_version_config=@com_google_protobuf//.github:host_xcodes
\ No newline at end of file
+common --xcode_version_config=@com_google_protobuf//.github:host_xcodes
diff --git a/conformance/binary_json_conformance_suite.cc b/conformance/binary_json_conformance_suite.cc
index 1d2c29800608..1d42c08e1468 100644
--- a/conformance/binary_json_conformance_suite.cc
+++ b/conformance/binary_json_conformance_suite.cc
@@ -3470,12 +3470,11 @@ BinaryAndJsonConformanceSuiteImpl<MessageType>::GetFieldForOneofType(
 template <typename MessageType>
 std::string BinaryAndJsonConformanceSuiteImpl<MessageType>::SyntaxIdentifier()
     const {
-  if constexpr (std::is_same<MessageType, TestAllTypesProto2>::value) {
+  if (std::is_same<MessageType, TestAllTypesProto2>::value) {
     return "Proto2";
-  } else if constexpr (std::is_same<MessageType, TestAllTypesProto3>::value) {
+  } else if (std::is_same<MessageType, TestAllTypesProto3>::value) {
     return "Proto3";
-  } else if constexpr (std::is_same<MessageType,
-                                    TestAllTypesProto2Editions>::value) {
+  } else if (std::is_same<MessageType, TestAllTypesProto2Editions>::value) {
     return "Editions_Proto2";
   } else {
     return "Editions_Proto3";
diff --git a/ruby/ext/google/protobuf_c/convert.c b/ruby/ext/google/protobuf_c/convert.c
index 90db70ebbde8..2b2244b0dcca 100644
--- a/ruby/ext/google/protobuf_c/convert.c
+++ b/ruby/ext/google/protobuf_c/convert.c
@@ -228,7 +228,8 @@ upb_MessageValue Convert_RubyToUpb(VALUE value, const char* name,
           ret.uint64_val = NUM2ULL(value);
           break;
         default:
-          break;
+          rb_raise(cTypeError, "Convert_RubyToUpb(): Unexpected type %d",
+                   (int)type_info.type);
       }
       break;
     default:
diff --git a/rust/cpp_kernel/map.cc b/rust/cpp_kernel/map.cc
index 2418c7274ccd..b1eca654688c 100644
--- a/rust/cpp_kernel/map.cc
+++ b/rust/cpp_kernel/map.cc
@@ -31,10 +31,10 @@ __PB_RUST_EXPOSE_SCALAR_MAP_METHODS_FOR_VALUE_TYPE(int64_t, i64, int64_t,
 __PB_RUST_EXPOSE_SCALAR_MAP_METHODS_FOR_VALUE_TYPE(
     std::string, ProtoBytes, google::protobuf::rust::PtrAndLen, std::string*,
     std::move(*value),
-    google::protobuf::rust::PtrAndLen(cpp_value.data(), cpp_value.size()));
+    (google::protobuf::rust::PtrAndLen{cpp_value.data(), cpp_value.size()}));
 __PB_RUST_EXPOSE_SCALAR_MAP_METHODS_FOR_VALUE_TYPE(
     std::string, ProtoString, google::protobuf::rust::PtrAndLen, std::string*,
     std::move(*value),
-    google::protobuf::rust::PtrAndLen(cpp_value.data(), cpp_value.size()));
+    (google::protobuf::rust::PtrAndLen{cpp_value.data(), cpp_value.size()}));
 
 }  // extern "C"
diff --git a/rust/cpp_kernel/map.h b/rust/cpp_kernel/map.h
index 2f0a8a82ab86..5e548949619e 100644
--- a/rust/cpp_kernel/map.h
+++ b/rust/cpp_kernel/map.h
@@ -85,7 +85,7 @@
   __PB_RUST_EXPOSE_SCALAR_MAP_METHODS(                                      \
       std::string, ProtoString, google::protobuf::rust::PtrAndLen,                    \
       std::string(key.ptr, key.len),                                        \
-      google::protobuf::rust::PtrAndLen(cpp_key.data(), cpp_key.size()), value_ty,    \
+      (google::protobuf::rust::PtrAndLen{cpp_key.data(), cpp_key.size()}), value_ty,  \
       rust_value_ty, ffi_view_ty, ffi_value_ty, to_cpp_value, to_ffi_value);
 
 #endif  // GOOGLE_PROTOBUF_RUST_CPP_KERNEL_MAP_H__
diff --git a/rust/cpp_kernel/repeated.cc b/rust/cpp_kernel/repeated.cc
index 79654fbad207..bb9ad004c791 100644
--- a/rust/cpp_kernel/repeated.cc
+++ b/rust/cpp_kernel/repeated.cc
@@ -77,7 +77,7 @@ expose_repeated_field_methods(int64_t, i64);
   google::protobuf::rust::PtrAndLen proto2_rust_RepeatedField_##ty##_get(      \
       google::protobuf::RepeatedPtrField<std::string>* r, size_t index) {      \
     const std::string& s = r->Get(index);                            \
-    return google::protobuf::rust::PtrAndLen(s.data(), s.size());              \
+    return google::protobuf::rust::PtrAndLen{s.data(), s.size()};              \
   }                                                                  \
   void proto2_rust_RepeatedField_##ty##_set(                         \
       google::protobuf::RepeatedPtrField<std::string>* r, size_t index,        \
diff --git a/rust/cpp_kernel/strings.cc b/rust/cpp_kernel/strings.cc
index c835a8a2219e..af29ddeaf430 100644
--- a/rust/cpp_kernel/strings.cc
+++ b/rust/cpp_kernel/strings.cc
@@ -33,6 +33,6 @@ std::string* proto2_rust_cpp_new_string(google::protobuf::rust::PtrAndLen src) {
 void proto2_rust_cpp_delete_string(std::string* str) { delete str; }
 
 google::protobuf::rust::PtrAndLen proto2_rust_cpp_string_to_view(std::string* str) {
-  return google::protobuf::rust::PtrAndLen(str->data(), str->length());
+  return google::protobuf::rust::PtrAndLen{str->data(), str->length()};
 }
 }
diff --git a/rust/cpp_kernel/strings.h b/rust/cpp_kernel/strings.h
index 8b51cdedb0a4..b3302a191972 100644
--- a/rust/cpp_kernel/strings.h
+++ b/rust/cpp_kernel/strings.h
@@ -22,8 +22,6 @@ struct PtrAndLen {
   /// Borrows the memory.
   const char* ptr;
   size_t len;
-
-  PtrAndLen(const char* ptr, size_t len) : ptr(ptr), len(len) {}
 };
 
 // Represents an owned string for FFI purposes.
diff --git a/src/google/protobuf/BUILD.bazel b/src/google/protobuf/BUILD.bazel
index ce1d5e8dbee3..e845839f40f2 100644
--- a/src/google/protobuf/BUILD.bazel
+++ b/src/google/protobuf/BUILD.bazel
@@ -1047,6 +1047,7 @@ cc_test(
     name = "string_view_test",
     srcs = ["string_view_test.cc"],
     deps = [
+        ":port",
         ":protobuf",
         ":unittest_string_view_cc_proto",
         "@com_google_absl//absl/strings:string_view",
diff --git a/src/google/protobuf/descriptor_database_unittest.cc b/src/google/protobuf/descriptor_database_unittest.cc
index 80e907def90a..7b24257244e8 100644
--- a/src/google/protobuf/descriptor_database_unittest.cc
+++ b/src/google/protobuf/descriptor_database_unittest.cc
@@ -446,14 +446,14 @@ TEST_P(DescriptorDatabaseTest, ConflictingExtensionError) {
       "            extendee: \".Foo\" }");
 }
 
-INSTANTIATE_TEST_CASE_P(
+INSTANTIATE_TEST_SUITE_P(
     Simple, DescriptorDatabaseTest,
     testing::Values(&SimpleDescriptorDatabaseTestCase::New));
-INSTANTIATE_TEST_CASE_P(
+INSTANTIATE_TEST_SUITE_P(
     MemoryConserving, DescriptorDatabaseTest,
     testing::Values(&EncodedDescriptorDatabaseTestCase::New));
-INSTANTIATE_TEST_CASE_P(Pool, DescriptorDatabaseTest,
-                        testing::Values(&DescriptorPoolDatabaseTestCase::New));
+INSTANTIATE_TEST_SUITE_P(Pool, DescriptorDatabaseTest,
+                         testing::Values(&DescriptorPoolDatabaseTestCase::New));
 
 TEST(EncodedDescriptorDatabaseExtraTest, FindNameOfFileContainingSymbol) {
   // Create two files, one of which is in two parts.
diff --git a/src/google/protobuf/string_view_test.cc b/src/google/protobuf/string_view_test.cc
index 1cdb860d9441..d348f1fbee87 100644
--- a/src/google/protobuf/string_view_test.cc
+++ b/src/google/protobuf/string_view_test.cc
@@ -12,6 +12,9 @@
 #include "google/protobuf/text_format.h"
 #include "google/protobuf/unittest_string_view.pb.h"
 
+// Must be included last.
+#include "google/protobuf/port_def.inc"
+
 namespace google {
 namespace protobuf {
 namespace {
@@ -284,10 +287,12 @@ TEST(StringViewFieldTest, RepeatedSetAndGetByReflection) {
   }
 
   // MutableRepeatedPtrField().
+  PROTOBUF_IGNORE_DEPRECATION_START;
   for (auto& it :
        *reflection->MutableRepeatedPtrField<std::string>(&message, field)) {
     it.append(it);
   }
+  PROTOBUF_IGNORE_DEPRECATION_STOP;
   {
     const auto& rep_str =
         reflection->GetRepeatedFieldRef<std::string>(message, field);
@@ -309,3 +314,5 @@ TEST(StringViewFieldTest, RepeatedSetAndGetByReflection) {
 }  // namespace
 }  // namespace protobuf
 }  // namespace google
+
+#include "google/protobuf/port_undef.inc"
diff --git a/third_party/zlib.BUILD b/third_party/zlib.BUILD
index faab8f5e8ba0..85a97c5d6ab7 100644
--- a/third_party/zlib.BUILD
+++ b/third_party/zlib.BUILD
@@ -59,6 +59,10 @@ cc_library(
     hdrs = _ZLIB_PREFIXED_HEADERS,
     copts = select({
         "@platforms//os:windows": [],
+        "@platforms//os:macos": [
+            "-Wno-unused-variable",
+            "-Wno-implicit-function-declaration",
+        ],
         "//conditions:default": [
             "-Wno-deprecated-non-prototype",
             "-Wno-unused-variable",
diff --git a/upb/io/zero_copy_stream_test.cc b/upb/io/zero_copy_stream_test.cc
index 392d924848b5..b7378d402b61 100644
--- a/upb/io/zero_copy_stream_test.cc
+++ b/upb/io/zero_copy_stream_test.cc
@@ -45,12 +45,6 @@ class IoTest : public testing::Test {
   // WriteStuff() writes.
   void ReadStuff(upb_ZeroCopyInputStream* input, bool read_eof = true);
 
-  // Similar to WriteStuff, but performs more sophisticated testing.
-  int WriteStuffLarge(upb_ZeroCopyOutputStream* output);
-  // Reads and tests a stream that should have been written to
-  // via WriteStuffLarge().
-  void ReadStuffLarge(upb_ZeroCopyInputStream* input);
-
   static const int kBlockSizes[];
   static const int kBlockSizeCount;
 };
@@ -157,35 +151,6 @@ void IoTest::ReadStuff(upb_ZeroCopyInputStream* input, bool read_eof) {
   }
 }
 
-int IoTest::WriteStuffLarge(upb_ZeroCopyOutputStream* output) {
-  WriteString(output, "Hello world!\n");
-  WriteString(output, "Some te");
-  WriteString(output, "xt.  Blah blah.");
-  WriteString(output, std::string(100000, 'x'));  // A very long string
-  WriteString(output, std::string(100000, 'y'));  // A very long string
-  WriteString(output, "01234567890123456789");
-
-  const int result = upb_ZeroCopyOutputStream_ByteCount(output);
-  EXPECT_EQ(result, 200055);
-  return result;
-}
-
-// Reads text from an input stream and expects it to match what WriteStuff()
-// writes.
-void IoTest::ReadStuffLarge(upb_ZeroCopyInputStream* input) {
-  ReadString(input, "Hello world!\nSome text.  ");
-  EXPECT_TRUE(upb_ZeroCopyInputStream_Skip(input, 5));
-  ReadString(input, "blah.");
-  EXPECT_TRUE(upb_ZeroCopyInputStream_Skip(input, 100000 - 10));
-  ReadString(input, std::string(10, 'x') + std::string(100000 - 20000, 'y'));
-  EXPECT_TRUE(upb_ZeroCopyInputStream_Skip(input, 20000 - 10));
-  ReadString(input, "yyyyyyyyyy01234567890123456789");
-  EXPECT_EQ(upb_ZeroCopyInputStream_ByteCount(input), 200055);
-
-  uint8_t byte;
-  EXPECT_EQ(ReadFromInput(input, &byte, 1), 0);
-}
-
 // ===================================================================
 
 TEST_F(IoTest, ArrayIo) {
diff --git a/upb/wire/eps_copy_input_stream_test.cc b/upb/wire/eps_copy_input_stream_test.cc
index c28d1457e474..c1c5dc76cc50 100644
--- a/upb/wire/eps_copy_input_stream_test.cc
+++ b/upb/wire/eps_copy_input_stream_test.cc
@@ -281,7 +281,7 @@ TEST(EpsCopyInputStreamTest, ZeroSize) {
 // }
 //
 // // Test with:
-// //  $ blaze run --config=fuzztest third_party/upb:eps_copy_input_stream_test \
+// //  $ bazel run --config=fuzztest third_party/upb:eps_copy_input_stream_test
 // //   -- --gunit_fuzz=
 // FUZZ_TEST(EpsCopyFuzzTest, TestAgainstFakeStream)
 //     .WithDomains(ArbitraryEpsCopyTestScript());