diff --git a/src/google/protobuf/io/tokenizer.cc b/src/google/protobuf/io/tokenizer.cc
index 6dc7d434f6d3d..4bf3efc84d40f 100644
--- a/src/google/protobuf/io/tokenizer.cc
+++ b/src/google/protobuf/io/tokenizer.cc
@@ -1177,7 +1177,9 @@ void Tokenizer::ParseStringAppend(const std::string& text,
   // downsize the output.
   const size_t new_len = text_size + output->size();
   if (new_len > output->capacity()) {
-    output->reserve(new_len);
+    // Make sure to use amortized growth if we already have a value.
+    output->reserve(
+        output->empty() ? new_len : std::max(new_len, output->capacity() * 2));
   }
 
   // Loop through the string copying characters to "output" and
diff --git a/src/google/protobuf/text_format_unittest.cc b/src/google/protobuf/text_format_unittest.cc
index 109257a2dc66f..28e84086e2c46 100644
--- a/src/google/protobuf/text_format_unittest.cc
+++ b/src/google/protobuf/text_format_unittest.cc
@@ -84,7 +84,9 @@ using ::absl_testing::StatusIs;
 using ::google::protobuf::internal::UnsetFieldsMetadataTextFormatTestUtil;
 using ::testing::_;
 using ::testing::AllOf;
+using ::testing::Gt;
 using ::testing::HasSubstr;
+using ::testing::Lt;
 using ::testing::UnorderedElementsAre;
 
 absl::string_view GetSubstring(absl::string_view input,
@@ -1391,6 +1393,7 @@ TEST_F(TextFormatTest, ParseConcatenatedString) {
   EXPECT_EQ("foobar", proto_.optional_string());
 }
 
+
 TEST_F(TextFormatTest, ParseFloatWithSuffix) {
   // Test that we can parse a floating-point value with 'f' appended to the
   // end.  This is needed for backwards-compatibility with proto1.