diff --git a/core/fxcrt/fx_basic_bstring.cpp b/core/fxcrt/fx_basic_bstring.cpp
index 1622c4b..e098d8f 100644
--- a/core/fxcrt/fx_basic_bstring.cpp
+++ b/core/fxcrt/fx_basic_bstring.cpp
@@ -276,20 +276,25 @@
   if (nNewLength == -1)
     nNewLength = FXSYS_strlen(m_pData->m_String);
 
+  nNewLength = std::min(nNewLength, m_pData->m_nAllocLength);
   if (nNewLength == 0) {
     clear();
     return;
   }
 
-  FXSYS_assert(nNewLength <= m_pData->m_nAllocLength);
-  ReallocBeforeWrite(nNewLength);
+  FXSYS_assert(m_pData->m_nRefs == 1);
   m_pData->m_nDataLength = nNewLength;
   m_pData->m_String[nNewLength] = 0;
+  if (m_pData->m_nAllocLength - nNewLength >= 32) {
+    // Over arbitrary threshold, so pay the price to relocate.  Force copy to
+    // always occur by holding a second reference to the string.
+    CFX_ByteString preserve(*this);
+    ReallocBeforeWrite(nNewLength);
+  }
 }
 
 void CFX_ByteString::Reserve(FX_STRSIZE len) {
   GetBuffer(len);
-  ReleaseBuffer(GetLength());
 }
 
 FX_CHAR* CFX_ByteString::GetBuffer(FX_STRSIZE nMinBufLength) {
diff --git a/core/fxcrt/fx_basic_bstring_unittest.cpp b/core/fxcrt/fx_basic_bstring_unittest.cpp
index ea7e17f..087c264 100644
--- a/core/fxcrt/fx_basic_bstring_unittest.cpp
+++ b/core/fxcrt/fx_basic_bstring_unittest.cpp
@@ -624,6 +624,83 @@
   }
 }
 
+TEST(fxcrt, ByteStringReserve) {
+  {
+    CFX_ByteString str;
+    str.Reserve(6);
+    const FX_CHAR* old_buffer = str.c_str();
+    str += "ABCDEF";
+    EXPECT_EQ(old_buffer, str.c_str());
+    str += "Blah Blah Blah Blah Blah Blah";
+    EXPECT_NE(old_buffer, str.c_str());
+  }
+  {
+    CFX_ByteString str("A");
+    str.Reserve(6);
+    const FX_CHAR* old_buffer = str.c_str();
+    str += "BCDEF";
+    EXPECT_EQ(old_buffer, str.c_str());
+    str += "Blah Blah Blah Blah Blah Blah";
+    EXPECT_NE(old_buffer, str.c_str());
+  }
+}
+
+TEST(fxcrt, ByteStringGetBuffer) {
+  {
+    CFX_ByteString str;
+    FX_CHAR* buffer = str.GetBuffer(12);
+    strcpy(buffer, "clams");
+    str.ReleaseBuffer();
+    EXPECT_EQ("clams", str);
+  }
+  {
+    CFX_ByteString str("cl");
+    FX_CHAR* buffer = str.GetBuffer(12);
+    strcpy(buffer + 2, "ams");
+    str.ReleaseBuffer();
+    EXPECT_EQ("clams", str);
+  }
+}
+
+TEST(fxcrt, ByteStringReleaseBuffer) {
+  {
+    CFX_ByteString str;
+    str.Reserve(12);
+    str += "clams";
+    const FX_CHAR* old_buffer = str.c_str();
+    str.ReleaseBuffer(4);
+    EXPECT_EQ(old_buffer, str.c_str());
+    EXPECT_EQ("clam", str);
+  }
+  {
+    CFX_ByteString str("c");
+    str.Reserve(12);
+    str += "lams";
+    const FX_CHAR* old_buffer = str.c_str();
+    str.ReleaseBuffer(4);
+    EXPECT_EQ(old_buffer, str.c_str());
+    EXPECT_EQ("clam", str);
+  }
+  {
+    CFX_ByteString str;
+    str.Reserve(200);
+    str += "clams";
+    const FX_CHAR* old_buffer = str.c_str();
+    str.ReleaseBuffer(4);
+    EXPECT_NE(old_buffer, str.c_str());
+    EXPECT_EQ("clam", str);
+  }
+  {
+    CFX_ByteString str("c");
+    str.Reserve(200);
+    str += "lams";
+    const FX_CHAR* old_buffer = str.c_str();
+    str.ReleaseBuffer(4);
+    EXPECT_NE(old_buffer, str.c_str());
+    EXPECT_EQ("clam", str);
+  }
+}
+
 TEST(fxcrt, ByteStringCNotNull) {
   CFX_ByteStringC string3("abc");
   CFX_ByteStringC string6("abcdef");
diff --git a/core/fxcrt/fx_basic_wstring.cpp b/core/fxcrt/fx_basic_wstring.cpp
index f3b430c..38fd15e 100644
--- a/core/fxcrt/fx_basic_wstring.cpp
+++ b/core/fxcrt/fx_basic_wstring.cpp
@@ -224,20 +224,25 @@
   if (nNewLength == -1)
     nNewLength = FXSYS_wcslen(m_pData->m_String);
 
+  nNewLength = std::min(nNewLength, m_pData->m_nAllocLength);
   if (nNewLength == 0) {
     clear();
     return;
   }
 
-  FXSYS_assert(nNewLength <= m_pData->m_nAllocLength);
-  ReallocBeforeWrite(nNewLength);
+  FXSYS_assert(m_pData->m_nRefs == 1);
   m_pData->m_nDataLength = nNewLength;
   m_pData->m_String[nNewLength] = 0;
+  if (m_pData->m_nAllocLength - nNewLength >= 32) {
+    // Over arbitrary threshold, so pay the price to relocate.  Force copy to
+    // always occur by holding a second reference to the string.
+    CFX_WideString preserve(*this);
+    ReallocBeforeWrite(nNewLength);
+  }
 }
 
 void CFX_WideString::Reserve(FX_STRSIZE len) {
   GetBuffer(len);
-  ReleaseBuffer(GetLength());
 }
 
 FX_WCHAR* CFX_WideString::GetBuffer(FX_STRSIZE nMinBufLength) {
diff --git a/core/fxcrt/fx_basic_wstring_unittest.cpp b/core/fxcrt/fx_basic_wstring_unittest.cpp
index 708556a..02281af 100644
--- a/core/fxcrt/fx_basic_wstring_unittest.cpp
+++ b/core/fxcrt/fx_basic_wstring_unittest.cpp
@@ -591,6 +591,83 @@
   }
 }
 
+TEST(fxcrt, WideStringReserve) {
+  {
+    CFX_WideString str;
+    str.Reserve(6);
+    const FX_WCHAR* old_buffer = str.c_str();
+    str += L"ABCDEF";
+    EXPECT_EQ(old_buffer, str.c_str());
+    str += L"Blah Blah Blah Blah Blah Blah";
+    EXPECT_NE(old_buffer, str.c_str());
+  }
+  {
+    CFX_WideString str(L"A");
+    str.Reserve(6);
+    const FX_WCHAR* old_buffer = str.c_str();
+    str += L"BCDEF";
+    EXPECT_EQ(old_buffer, str.c_str());
+    str += L"Blah Blah Blah Blah Blah Blah";
+    EXPECT_NE(old_buffer, str.c_str());
+  }
+}
+
+TEST(fxcrt, WideStringGetBuffer) {
+  {
+    CFX_WideString str;
+    FX_WCHAR* buffer = str.GetBuffer(12);
+    wcscpy(buffer, L"clams");
+    str.ReleaseBuffer();
+    EXPECT_EQ(L"clams", str);
+  }
+  {
+    CFX_WideString str(L"cl");
+    FX_WCHAR* buffer = str.GetBuffer(12);
+    wcscpy(buffer + 2, L"ams");
+    str.ReleaseBuffer();
+    EXPECT_EQ(L"clams", str);
+  }
+}
+
+TEST(fxcrt, WideStringReleaseBuffer) {
+  {
+    CFX_WideString str;
+    str.Reserve(12);
+    str += L"clams";
+    const FX_WCHAR* old_buffer = str.c_str();
+    str.ReleaseBuffer(4);
+    EXPECT_EQ(old_buffer, str.c_str());
+    EXPECT_EQ(L"clam", str);
+  }
+  {
+    CFX_WideString str(L"c");
+    str.Reserve(12);
+    str += L"lams";
+    const FX_WCHAR* old_buffer = str.c_str();
+    str.ReleaseBuffer(4);
+    EXPECT_EQ(old_buffer, str.c_str());
+    EXPECT_EQ(L"clam", str);
+  }
+  {
+    CFX_WideString str;
+    str.Reserve(200);
+    str += L"clams";
+    const FX_WCHAR* old_buffer = str.c_str();
+    str.ReleaseBuffer(4);
+    EXPECT_NE(old_buffer, str.c_str());
+    EXPECT_EQ(L"clam", str);
+  }
+  {
+    CFX_WideString str(L"c");
+    str.Reserve(200);
+    str += L"lams";
+    const FX_WCHAR* old_buffer = str.c_str();
+    str.ReleaseBuffer(4);
+    EXPECT_NE(old_buffer, str.c_str());
+    EXPECT_EQ(L"clam", str);
+  }
+}
+
 TEST(fxcrt, WideStringUTF16LE_Encode) {
   struct UTF16LEEncodeCase {
     CFX_WideString ws;