diff --git a/rtc_base/strings/string_builder.cc b/rtc_base/strings/string_builder.cc
index 499fb9a..528f099 100644
--- a/rtc_base/strings/string_builder.cc
+++ b/rtc_base/strings/string_builder.cc
@@ -18,4 +18,95 @@
   RTC_DCHECK(IsConsistent());
 }
 
+SimpleStringBuilder& SimpleStringBuilder::operator<<(const char* str) {
+  return Append(str);
+}
+
+SimpleStringBuilder& SimpleStringBuilder::operator<<(char ch) {
+  return Append(&ch, 1);
+}
+
+SimpleStringBuilder& SimpleStringBuilder::operator<<(const std::string& str) {
+  return Append(str.c_str(), str.length());
+}
+
+// Numeric conversion routines.
+//
+// We use std::[v]snprintf instead of std::to_string because:
+// * std::to_string relies on the current locale for formatting purposes,
+//   and therefore concurrent calls to std::to_string from multiple threads
+//   may result in partial serialization of calls
+// * snprintf allows us to print the number directly into our buffer.
+// * avoid allocating a std::string (potential heap alloc).
+// TODO(tommi): Switch to std::to_chars in C++17.
+
+SimpleStringBuilder& SimpleStringBuilder::operator<<(int i) {
+  return AppendFormat("%d", i);
+}
+
+SimpleStringBuilder& SimpleStringBuilder::operator<<(unsigned i) {
+  return AppendFormat("%u", i);
+}
+
+SimpleStringBuilder& SimpleStringBuilder::operator<<(long i) {  // NOLINT
+  return AppendFormat("%ld", i);
+}
+
+SimpleStringBuilder& SimpleStringBuilder::operator<<(long long i) {  // NOLINT
+  return AppendFormat("%lld", i);
+}
+
+SimpleStringBuilder& SimpleStringBuilder::operator<<(
+    unsigned long i) {  // NOLINT
+  return AppendFormat("%lu", i);
+}
+
+SimpleStringBuilder& SimpleStringBuilder::operator<<(
+    unsigned long long i) {  // NOLINT
+  return AppendFormat("%llu", i);
+}
+
+SimpleStringBuilder& SimpleStringBuilder::operator<<(float f) {
+  return AppendFormat("%f", f);
+}
+
+SimpleStringBuilder& SimpleStringBuilder::operator<<(double f) {
+  return AppendFormat("%f", f);
+}
+
+SimpleStringBuilder& SimpleStringBuilder::operator<<(long double f) {
+  return AppendFormat("%Lf", f);
+}
+
+SimpleStringBuilder& SimpleStringBuilder::AppendFormat(const char* fmt, ...) {
+  va_list args;
+  va_start(args, fmt);
+  const int len =
+      std::vsnprintf(&buffer_[size_], buffer_.size() - size_, fmt, args);
+  if (len >= 0) {
+    const size_t chars_added = rtc::SafeMin(len, buffer_.size() - 1 - size_);
+    size_ += chars_added;
+    RTC_DCHECK_EQ(len, chars_added) << "Buffer size was insufficient";
+  } else {
+    // This should never happen, but we're paranoid, so re-write the
+    // terminator in case vsnprintf() overwrote it.
+    RTC_NOTREACHED();
+    buffer_[size_] = '\0';
+  }
+  va_end(args);
+  RTC_DCHECK(IsConsistent());
+  return *this;
+}
+
+SimpleStringBuilder& SimpleStringBuilder::Append(const char* str,
+                                                 size_t length) {
+  const size_t chars_added =
+      rtc::strcpyn(&buffer_[size_], buffer_.size() - size_, str, length);
+  size_ += chars_added;
+  RTC_DCHECK_EQ(chars_added, length == SIZE_UNKNOWN ? std::strlen(str) : length)
+      << "Buffer size was insufficient";
+  RTC_DCHECK(IsConsistent());
+  return *this;
+}
+
 }  // namespace rtc
diff --git a/rtc_base/strings/string_builder.h b/rtc_base/strings/string_builder.h
index b450a99..d095385 100644
--- a/rtc_base/strings/string_builder.h
+++ b/rtc_base/strings/string_builder.h
@@ -33,51 +33,18 @@
   SimpleStringBuilder(const SimpleStringBuilder&) = delete;
   SimpleStringBuilder& operator=(const SimpleStringBuilder&) = delete;
 
-  SimpleStringBuilder& operator<<(const char* str) { return Append(str); }
-
-  SimpleStringBuilder& operator<<(char ch) { return Append(&ch, 1); }
-
-  SimpleStringBuilder& operator<<(const std::string& str) {
-    return Append(str.c_str(), str.length());
-  }
-
-  // Numeric conversion routines.
-  //
-  // We use std::[v]snprintf instead of std::to_string because:
-  // * std::to_string relies on the current locale for formatting purposes,
-  //   and therefore concurrent calls to std::to_string from multiple threads
-  //   may result in partial serialization of calls
-  // * snprintf allows us to print the number directly into our buffer.
-  // * avoid allocating a std::string (potential heap alloc).
-  // TODO(tommi): Switch to std::to_chars in C++17.
-
-  SimpleStringBuilder& operator<<(int i) { return AppendFormat("%d", i); }
-
-  SimpleStringBuilder& operator<<(unsigned i) { return AppendFormat("%u", i); }
-
-  SimpleStringBuilder& operator<<(long i) {  // NOLINT
-    return AppendFormat("%ld", i);
-  }
-
-  SimpleStringBuilder& operator<<(long long i) {  // NOLINT
-    return AppendFormat("%lld", i);
-  }
-
-  SimpleStringBuilder& operator<<(unsigned long i) {  // NOLINT
-    return AppendFormat("%lu", i);
-  }
-
-  SimpleStringBuilder& operator<<(unsigned long long i) {  // NOLINT
-    return AppendFormat("%llu", i);
-  }
-
-  SimpleStringBuilder& operator<<(float f) { return AppendFormat("%f", f); }
-
-  SimpleStringBuilder& operator<<(double f) { return AppendFormat("%f", f); }
-
-  SimpleStringBuilder& operator<<(long double f) {
-    return AppendFormat("%Lf", f);
-  }
+  SimpleStringBuilder& operator<<(const char* str);
+  SimpleStringBuilder& operator<<(char ch);
+  SimpleStringBuilder& operator<<(const std::string& str);
+  SimpleStringBuilder& operator<<(int i);
+  SimpleStringBuilder& operator<<(unsigned i);
+  SimpleStringBuilder& operator<<(long i);                // NOLINT
+  SimpleStringBuilder& operator<<(long long i);           // NOLINT
+  SimpleStringBuilder& operator<<(unsigned long i);       // NOLINT
+  SimpleStringBuilder& operator<<(unsigned long long i);  // NOLINT
+  SimpleStringBuilder& operator<<(float f);
+  SimpleStringBuilder& operator<<(double f);
+  SimpleStringBuilder& operator<<(long double f);
 
   // Returns a pointer to the built string. The name |str()| is borrowed for
   // compatibility reasons as we replace usage of stringstream throughout the
@@ -93,38 +60,11 @@
   __attribute__((__format__(__printf__, 2, 3)))
 #endif
   SimpleStringBuilder&
-  AppendFormat(const char* fmt, ...) {
-    va_list args;
-    va_start(args, fmt);
-    const int len =
-        std::vsnprintf(&buffer_[size_], buffer_.size() - size_, fmt, args);
-    if (len >= 0) {
-      const size_t chars_added = rtc::SafeMin(len, buffer_.size() - 1 - size_);
-      size_ += chars_added;
-      RTC_DCHECK_EQ(len, chars_added) << "Buffer size was insufficient";
-    } else {
-      // This should never happen, but we're paranoid, so re-write the
-      // terminator in case vsnprintf() overwrote it.
-      RTC_NOTREACHED();
-      buffer_[size_] = '\0';
-    }
-    va_end(args);
-    RTC_DCHECK(IsConsistent());
-    return *this;
-  }
+  AppendFormat(const char* fmt, ...);
 
   // 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 = SIZE_UNKNOWN) {
-    const size_t chars_added =
-        rtc::strcpyn(&buffer_[size_], buffer_.size() - size_, str, length);
-    size_ += chars_added;
-    RTC_DCHECK_EQ(chars_added,
-                  length == SIZE_UNKNOWN ? std::strlen(str) : length)
-        << "Buffer size was insufficient";
-    RTC_DCHECK(IsConsistent());
-    return *this;
-  }
+  SimpleStringBuilder& Append(const char* str, size_t length = SIZE_UNKNOWN);
 
  private:
   bool IsConsistent() const {