diff --git a/media/sctp/sctp_transport.cc b/media/sctp/sctp_transport.cc
index b9e7ae318d..8bcec41a28 100644
--- a/media/sctp/sctp_transport.cc
+++ b/media/sctp/sctp_transport.cc
@@ -36,7 +36,6 @@ enum PreservedErrno {
 #include "rtc_base/helpers.h"
 #include "rtc_base/logging.h"
 #include "rtc_base/numerics/safe_conversions.h"
-#include "rtc_base/string_utils.h"
 #include "rtc_base/thread_checker.h"
 #include "rtc_base/trace_event.h"
 #include "usrsctplib/usrsctp.h"
diff --git a/modules/audio_device/win/core_audio_utility_win.h b/modules/audio_device/win/core_audio_utility_win.h
index 6e2c85bf6f..0ef16ff9cb 100644
--- a/modules/audio_device/win/core_audio_utility_win.h
+++ b/modules/audio_device/win/core_audio_utility_win.h
@@ -26,7 +26,6 @@
 #include "modules/audio_device/audio_device_name.h"
 #include "modules/audio_device/include/audio_device_defines.h"
 #include "rtc_base/logging.h"
-#include "rtc_base/string_utils.h"
 
 #pragma comment(lib, "Avrt.lib")
 
diff --git a/p2p/base/port.cc b/p2p/base/port.cc
index b6fca242ed..645cc650cf 100644
--- a/p2p/base/port.cc
+++ b/p2p/base/port.cc
@@ -29,7 +29,6 @@
 #include "rtc_base/network.h"
 #include "rtc_base/numerics/safe_minmax.h"
 #include "rtc_base/string_encode.h"
-#include "rtc_base/string_utils.h"
 #include "rtc_base/third_party/base64/base64.h"
 #include "system_wrappers/include/field_trial.h"
 
diff --git a/pc/webrtc_sdp.cc b/pc/webrtc_sdp.cc
index a6165eb3d4..f8c9e70739 100644
--- a/pc/webrtc_sdp.cc
+++ b/pc/webrtc_sdp.cc
@@ -45,7 +45,6 @@
 #include "rtc_base/checks.h"
 #include "rtc_base/logging.h"
 #include "rtc_base/message_digest.h"
-#include "rtc_base/string_utils.h"
 #include "rtc_base/strings/string_builder.h"
 #include "rtc_base/third_party/base64/base64.h"
 
diff --git a/rtc_base/http_common.cc b/rtc_base/http_common.cc
index 10cfb3a14e..0456eeaa1c 100644
--- a/rtc_base/http_common.cc
+++ b/rtc_base/http_common.cc
@@ -30,7 +30,6 @@
 #include "rtc_base/logging.h"
 #include "rtc_base/message_digest.h"
 #include "rtc_base/socket_address.h"
-#include "rtc_base/string_utils.h"
 #include "rtc_base/strings/string_builder.h"
 #include "rtc_base/third_party/base64/base64.h"  // for Base64
 #include "rtc_base/zero_memory.h"                // for ExplicitZeroMemory
diff --git a/rtc_base/strings/string_builder.cc b/rtc_base/strings/string_builder.cc
index 0583dc789a..adf4fa9e81 100644
--- a/rtc_base/strings/string_builder.cc
+++ b/rtc_base/strings/string_builder.cc
@@ -25,7 +25,7 @@ SimpleStringBuilder::SimpleStringBuilder(rtc::ArrayView<char> buffer)
 }
 
 SimpleStringBuilder& SimpleStringBuilder::operator<<(const char* str) {
-  return Append(str, strlen(str));
+  return Append(str);
 }
 
 SimpleStringBuilder& SimpleStringBuilder::operator<<(char ch) {
@@ -106,12 +106,11 @@ SimpleStringBuilder& SimpleStringBuilder::AppendFormat(const char* fmt, ...) {
 
 SimpleStringBuilder& SimpleStringBuilder::Append(const char* str,
                                                  size_t length) {
-  RTC_DCHECK_LT(size_ + length, buffer_.size())
-      << "Buffer size was insufficient";
-  const size_t chars_added = rtc::SafeMin(length, buffer_.size() - size_ - 1);
-  memcpy(&buffer_[size_], str, chars_added);
+  const size_t chars_added =
+      rtc::strcpyn(&buffer_[size_], buffer_.size() - size_, str, length);
   size_ += chars_added;
-  buffer_[size_] = '\0';
+  RTC_DCHECK_EQ(chars_added, length == SIZE_UNKNOWN ? std::strlen(str) : length)
+      << "Buffer size was insufficient";
   RTC_DCHECK(IsConsistent());
   return *this;
 }
diff --git a/rtc_base/strings/string_builder.h b/rtc_base/strings/string_builder.h
index e528cf2f0e..7c45ac4ace 100644
--- a/rtc_base/strings/string_builder.h
+++ b/rtc_base/strings/string_builder.h
@@ -18,6 +18,7 @@
 #include "absl/strings/string_view.h"
 #include "api/array_view.h"
 #include "rtc_base/string_encode.h"
+#include "rtc_base/string_utils.h"
 
 namespace rtc {
 
@@ -63,7 +64,7 @@ class SimpleStringBuilder {
 
   // An alternate way from operator<<() to append a string. This variant is
   // slightly more efficient when the length of the string to append, is known.
-  SimpleStringBuilder& Append(const char* str, size_t length);
+  SimpleStringBuilder& Append(const char* str, size_t length = SIZE_UNKNOWN);
 
  private:
   bool IsConsistent() const {
diff --git a/sdk/android/native_unittests/stacktrace/stacktrace_unittest.cc b/sdk/android/native_unittests/stacktrace/stacktrace_unittest.cc
index 917dbc972f..4ea3c9f376 100644
--- a/sdk/android/native_unittests/stacktrace/stacktrace_unittest.cc
+++ b/sdk/android/native_unittests/stacktrace/stacktrace_unittest.cc
@@ -19,7 +19,6 @@
 #include "rtc_base/event.h"
 #include "rtc_base/logging.h"
 #include "rtc_base/platform_thread.h"
-#include "rtc_base/string_utils.h"
 #include "rtc_base/strings/string_builder.h"
 #include "rtc_base/system/inline.h"
 #include "system_wrappers/include/sleep.h"
diff --git a/test/logging/log_writer.h b/test/logging/log_writer.h
index db4a7371d0..9879eaa0df 100644
--- a/test/logging/log_writer.h
+++ b/test/logging/log_writer.h
@@ -10,7 +10,6 @@
 #ifndef TEST_LOGGING_LOG_WRITER_H_
 #define TEST_LOGGING_LOG_WRITER_H_
 
-#include <stdarg.h>
 #include <memory>
 #include <string>
 #include <utility>