1 files changed, 7 insertions, 4 deletions
diff --git a/core/fxcrt/cfx_string_c_template.h b/core/fxcrt/cfx_string_c_template.h
index 6a95a05d45..bc0fe1e0a0 100644
--- a/core/fxcrt/cfx_string_c_template.h
+++ b/core/fxcrt/cfx_string_c_template.h
@@ -119,8 +119,13 @@ class CFX_StringCTemplate {
   FX_STRSIZE GetLength() const { return m_Length; }
   bool IsEmpty() const { return m_Length == 0; }
 
-  UnsignedType GetAt(FX_STRSIZE index) const { return m_Ptr.Get()[index]; }
+  UnsignedType GetAt(FX_STRSIZE index) const {
+    ASSERT(index >= 0 && index < GetLength());
+    return m_Ptr.Get()[index];
+  }
+
   CharType CharAt(FX_STRSIZE index) const {
+    ASSERT(index >= 0 && index < GetLength());
     return static_cast<CharType>(m_Ptr.Get()[index]);
   }
 
@@ -159,9 +164,7 @@ class CFX_StringCTemplate {
     return CFX_StringCTemplate(m_Ptr.Get() + m_Length - count, count);
   }
 
-  const UnsignedType& operator[](size_t index) const {
-    return m_Ptr.Get()[index];
-  }
+  UnsignedType operator[](FX_STRSIZE index) const { return GetAt(index); }
 
   bool operator<(const CFX_StringCTemplate& that) const {
     int result = FXSYS_cmp(reinterpret_cast<const CharType*>(m_Ptr.Get()),