diff --git a/src/google/protobuf/compiler/cpp/cpp_enum_field.cc b/src/google/protobuf/compiler/cpp/cpp_enum_field.cc
index 6b9a5eb1dbc0..cdcd9a6da225 100644
--- a/src/google/protobuf/compiler/cpp/cpp_enum_field.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_enum_field.cc
@@ -496,7 +496,7 @@ void RepeatedEnumFieldGenerator::GenerateConstinitInitializer(
   format("$name$_()");
   if (descriptor_->is_packed() &&
       HasGeneratedMethods(descriptor_->file(), options_)) {
-    format("\n, _$name$_cached_byte_size_()");
+    format("\n, _$name$_cached_byte_size_(0)");
   }
 }
 
diff --git a/src/google/protobuf/compiler/cpp/cpp_primitive_field.cc b/src/google/protobuf/compiler/cpp/cpp_primitive_field.cc
index 98ba8a698e65..9664586f2853 100644
--- a/src/google/protobuf/compiler/cpp/cpp_primitive_field.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_primitive_field.cc
@@ -486,7 +486,7 @@ void RepeatedPrimitiveFieldGenerator::GenerateConstinitInitializer(
   format("$name$_()");
   if (descriptor_->is_packed() && FixedSize(descriptor_->type()) == -1 &&
       HasGeneratedMethods(descriptor_->file(), options_)) {
-    format("\n, _$name$_cached_byte_size_()");
+    format("\n, _$name$_cached_byte_size_(0)");
   }
 }
 
diff --git a/src/google/protobuf/descriptor.pb.cc b/src/google/protobuf/descriptor.pb.cc
index 8aef94cbf65f..86df8966c539 100644
--- a/src/google/protobuf/descriptor.pb.cc
+++ b/src/google/protobuf/descriptor.pb.cc
@@ -393,9 +393,9 @@ PROTOBUF_ATTRIBUTE_NO_DESTROY PROTOBUF_CONSTINIT UninterpretedOptionDefaultTypeI
 constexpr SourceCodeInfo_Location::SourceCodeInfo_Location(
   ::PROTOBUF_NAMESPACE_ID::internal::ConstantInitialized)
   : path_()
-  , _path_cached_byte_size_()
+  , _path_cached_byte_size_(0)
   , span_()
-  , _span_cached_byte_size_()
+  , _span_cached_byte_size_(0)
   , leading_detached_comments_()
   , leading_comments_(&::PROTOBUF_NAMESPACE_ID::internal::fixed_address_empty_string)
   , trailing_comments_(&::PROTOBUF_NAMESPACE_ID::internal::fixed_address_empty_string){}
@@ -423,7 +423,7 @@ PROTOBUF_ATTRIBUTE_NO_DESTROY PROTOBUF_CONSTINIT SourceCodeInfoDefaultTypeIntern
 constexpr GeneratedCodeInfo_Annotation::GeneratedCodeInfo_Annotation(
   ::PROTOBUF_NAMESPACE_ID::internal::ConstantInitialized)
   : path_()
-  , _path_cached_byte_size_()
+  , _path_cached_byte_size_(0)
   , source_file_(&::PROTOBUF_NAMESPACE_ID::internal::fixed_address_empty_string)
   , begin_(0)
   , end_(0){}
diff --git a/src/google/protobuf/io/coded_stream.h b/src/google/protobuf/io/coded_stream.h
index b6c11d27a217..1cf006832a7b 100644
--- a/src/google/protobuf/io/coded_stream.h
+++ b/src/google/protobuf/io/coded_stream.h
@@ -136,8 +136,10 @@
 #elif defined(__FreeBSD__)
 #include <sys/endian.h>  // __BYTE_ORDER
 #else
+#if !defined(__QNX__)
 #include <endian.h>  // __BYTE_ORDER
 #endif
+#endif
 #if ((defined(__LITTLE_ENDIAN__) && !defined(__BIG_ENDIAN__)) ||    \
      (defined(__BYTE_ORDER) && __BYTE_ORDER == __LITTLE_ENDIAN)) && \
     !defined(PROTOBUF_DISABLE_LITTLE_ENDIAN_OPT_FOR_TEST)
diff --git a/src/google/protobuf/stubs/mutex.h b/src/google/protobuf/stubs/mutex.h
index bff96814b441..79c9f6784894 100644
--- a/src/google/protobuf/stubs/mutex.h
+++ b/src/google/protobuf/stubs/mutex.h
@@ -116,7 +116,11 @@ class CallOnceInitializedMutex {
 // mutexes.
 class GOOGLE_PROTOBUF_CAPABILITY("mutex") PROTOBUF_EXPORT WrappedMutex {
  public:
+#if defined(__QNX__)
+  constexpr WrappedMutex() = default;
+#else
   constexpr WrappedMutex() {}
+#endif
   void Lock() GOOGLE_PROTOBUF_ACQUIRE() { mu_.lock(); }
   void Unlock() GOOGLE_PROTOBUF_RELEASE() { mu_.unlock(); }
   // Crash if this Mutex is not held exclusively by this thread.
diff --git a/src/google/protobuf/stubs/platform_macros.h b/src/google/protobuf/stubs/platform_macros.h
index ce1b1e365576..24799600dcf8 100644
--- a/src/google/protobuf/stubs/platform_macros.h
+++ b/src/google/protobuf/stubs/platform_macros.h
@@ -46,7 +46,11 @@
 #define GOOGLE_PROTOBUF_ARCH_32_BIT 1
 #elif defined(__QNX__)
 #define GOOGLE_PROTOBUF_ARCH_ARM_QNX 1
+#if defined(__aarch64__)
+#define GOOGLE_PROTOBUF_ARCH_64_BIT 1
+#else
 #define GOOGLE_PROTOBUF_ARCH_32_BIT 1
+#endif
 #elif defined(_M_ARM) || defined(__ARMEL__)
 #define GOOGLE_PROTOBUF_ARCH_ARM 1
 #define GOOGLE_PROTOBUF_ARCH_32_BIT 1
diff --git a/src/google/protobuf/stubs/port.h b/src/google/protobuf/stubs/port.h
index bead0af74306..d4d2736c8579 100644
--- a/src/google/protobuf/stubs/port.h
+++ b/src/google/protobuf/stubs/port.h
@@ -62,8 +62,10 @@
 #elif defined(__FreeBSD__)
 #include <sys/endian.h>  // __BYTE_ORDER
 #else
+#if !defined(__QNX__)
 #include <endian.h>  // __BYTE_ORDER
 #endif
+#endif
 #if ((defined(__LITTLE_ENDIAN__) && !defined(__BIG_ENDIAN__)) ||   \
      (defined(__BYTE_ORDER) && __BYTE_ORDER == __LITTLE_ENDIAN) || \
      (defined(BYTE_ORDER) && BYTE_ORDER == LITTLE_ENDIAN)) &&      \