diff --git a/rtc_base/openssl_adapter.cc b/rtc_base/openssl_adapter.cc
index d5c51ff495..a9e5858bca 100644
--- a/rtc_base/openssl_adapter.cc
+++ b/rtc_base/openssl_adapter.cc
@@ -44,7 +44,7 @@
 #include "rtc_base/openssl_identity.h"
 #endif
 #include "rtc_base/openssl_utility.h"
-#include "rtc_base/string_encode.h"
+#include "rtc_base/strings/string_builder.h"
 #include "rtc_base/thread.h"
 
 //////////////////////////////////////////////////////////////////////
@@ -166,6 +166,23 @@ static void LogSslError() {
 
 namespace rtc {
 
+namespace webrtc_openssl_adapter_internal {
+
+// Simple O(n^2) implementation is sufficient for current use case.
+std::string StrJoin(const std::vector<std::string>& list, char delimiter) {
+  RTC_CHECK(!list.empty());
+  StringBuilder sb;
+  sb << list[0];
+  for (size_t i = 1; i < list.size(); i++) {
+    sb.AppendFormat("%c", delimiter);
+    sb << list[i];
+  }
+  return sb.Release();
+}
+}  // namespace webrtc_openssl_adapter_internal
+
+using webrtc_openssl_adapter_internal::StrJoin;
+
 bool OpenSSLAdapter::InitializeSSL() {
   if (!SSL_library_init())
     return false;
@@ -354,7 +371,7 @@ int OpenSSLAdapter::BeginSSL() {
   }
 
   if (!elliptic_curves_.empty()) {
-    SSL_set1_curves_list(ssl_, rtc::join(elliptic_curves_, ':').c_str());
+    SSL_set1_curves_list(ssl_, StrJoin(elliptic_curves_, ':').c_str());
   }
 
   // Now that the initial config is done, transfer ownership of `bio` to the
diff --git a/rtc_base/openssl_adapter.h b/rtc_base/openssl_adapter.h
index d5e8b9e638..50ae44d7cc 100644
--- a/rtc_base/openssl_adapter.h
+++ b/rtc_base/openssl_adapter.h
@@ -37,6 +37,14 @@
 
 namespace rtc {
 
+namespace webrtc_openssl_adapter_internal {
+
+// Local definition, since absl::StrJoin is not allow-listed. Declared in header
+// file only for unittests.
+std::string StrJoin(const std::vector<std::string>& list, char delimiter);
+
+}  // namespace webrtc_openssl_adapter_internal
+
 class OpenSSLAdapter final : public SSLAdapter,
                              public MessageHandlerAutoCleanup {
  public:
diff --git a/rtc_base/openssl_adapter_unittest.cc b/rtc_base/openssl_adapter_unittest.cc
index 0805cba56c..21da777e7a 100644
--- a/rtc_base/openssl_adapter_unittest.cc
+++ b/rtc_base/openssl_adapter_unittest.cc
@@ -113,4 +113,19 @@ TEST(OpenSSLAdapterFactoryTest, CreateWorksWithCustomVerifier) {
   EXPECT_NE(simple_adapter, nullptr);
 }
 
+TEST(StrJoinTest, SingleElement) {
+  EXPECT_EQ(webrtc_openssl_adapter_internal::StrJoin({"a"}, ','), "a");
+}
+
+TEST(StrJoinTest, TwoElements) {
+  EXPECT_EQ(webrtc_openssl_adapter_internal::StrJoin({"first", "second"}, ':'),
+            "first:second");
+}
+
+TEST(StrJoinTest, WithEmptyElement) {
+  EXPECT_EQ(
+      webrtc_openssl_adapter_internal::StrJoin({"first", "", "second"}, ':'),
+      "first::second");
+}
+
 }  // namespace rtc
diff --git a/rtc_base/string_encode.cc b/rtc_base/string_encode.cc
index 5129b24473..84361ae142 100644
--- a/rtc_base/string_encode.cc
+++ b/rtc_base/string_encode.cc
@@ -174,28 +174,6 @@ bool tokenize_first(absl::string_view source,
   return true;
 }
 
-std::string join(const std::vector<std::string>& source, char delimiter) {
-  if (source.size() == 0) {
-    return std::string();
-  }
-  // Find length of the string to be returned to pre-allocate memory.
-  size_t source_string_length = 0;
-  for (size_t i = 0; i < source.size(); ++i) {
-    source_string_length += source[i].length();
-  }
-
-  // Build the joined string.
-  std::string joined_string;
-  joined_string.reserve(source_string_length + source.size() - 1);
-  for (size_t i = 0; i < source.size(); ++i) {
-    if (i != 0) {
-      joined_string += delimiter;
-    }
-    joined_string += source[i];
-  }
-  return joined_string;
-}
-
 std::vector<absl::string_view> split(absl::string_view source, char delimiter) {
   std::vector<absl::string_view> fields;
   size_t last = 0;
diff --git a/rtc_base/string_encode.h b/rtc_base/string_encode.h
index 3ed034bbb4..6bbb0088f3 100644
--- a/rtc_base/string_encode.h
+++ b/rtc_base/string_encode.h
@@ -43,10 +43,6 @@ size_t hex_decode_with_delimiter(ArrayView<char> buffer,
                                  absl::string_view source,
                                  char delimiter);
 
-// Joins the source vector of strings into a single string, with each
-// field in source being separated by delimiter. No trailing delimiter is added.
-std::string join(const std::vector<std::string>& source, char delimiter);
-
 // Splits the source string into multiple fields separated by delimiter,
 // with duplicates of delimiter creating empty fields. Empty input produces a
 // single, empty, field.