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# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License.  You may obtain a copy of the License at
#
#   http://www.apache.org/licenses/LICENSE-2.0
#
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--- a/src/google/protobuf/port_def.inc
+++ b/src/google/protobuf/port_def.inc
@@ -435,13 +435,15 @@
 # endif
 #else
-# if defined(__cpp_constinit) && !defined(__CYGWIN__)
+// Emscripten's libc++ std::string is not constexpr-constructible (heap alloc).
+# if defined(__cpp_constinit) && !defined(__CYGWIN__) && !defined(__EMSCRIPTEN__)
 #  define PROTOBUF_CONSTINIT constinit
 #  define PROTOBUF_CONSTEXPR constexpr
 #  define PROTOBUF_CONSTINIT_DEFAULT_INSTANCES
 // Some older Clang versions incorrectly raise an error about
 // constant-initializing weak default instance pointers. Versions 12.0 and
 // higher seem to work, except that XCode 12.5.1 shows the error even though it
 // uses Clang 12.0.5.
-#elif !defined(__CYGWIN__) && !defined(__MINGW32__) &&                 \
+#elif !defined(__CYGWIN__) && !defined(__MINGW32__) &&                  \
+    !defined(__EMSCRIPTEN__) &&                                         \
     ABSL_HAVE_CPP_ATTRIBUTE(clang::require_constant_initialization) && \
     ((defined(__APPLE__) && PROTOBUF_CLANG_MIN(13, 0)) ||              \
      (!defined(__APPLE__) && PROTOBUF_CLANG_MIN(12, 0)))