diff --git a/mozilla/string/obsolete/nsXPIDLString.cpp b/mozilla/string/obsolete/nsXPIDLString.cpp
index 0fd5778c39b..c18024ae2cc 100644
--- a/mozilla/string/obsolete/nsXPIDLString.cpp
+++ b/mozilla/string/obsolete/nsXPIDLString.cpp
@@ -128,7 +128,8 @@ nsXPIDLCString& nsXPIDLCString::operator =(const char* aCString)
     if (mBufOwner && mBuf)
         XPIDL_FREE(mBuf);
 	
-    mBuf = Copy(aCString);
+    if (aCString)
+        mBuf = Copy(aCString);
     mBufOwner = PR_TRUE;
     
     return *this;
diff --git a/mozilla/xpcom/ds/nsXPIDLString.cpp b/mozilla/xpcom/ds/nsXPIDLString.cpp
index 0fd5778c39b..c18024ae2cc 100644
--- a/mozilla/xpcom/ds/nsXPIDLString.cpp
+++ b/mozilla/xpcom/ds/nsXPIDLString.cpp
@@ -128,7 +128,8 @@ nsXPIDLCString& nsXPIDLCString::operator =(const char* aCString)
     if (mBufOwner && mBuf)
         XPIDL_FREE(mBuf);
 	
-    mBuf = Copy(aCString);
+    if (aCString)
+        mBuf = Copy(aCString);
     mBufOwner = PR_TRUE;
     
     return *this;
diff --git a/mozilla/xpcom/string/obsolete/nsXPIDLString.cpp b/mozilla/xpcom/string/obsolete/nsXPIDLString.cpp
index 0fd5778c39b..c18024ae2cc 100644
--- a/mozilla/xpcom/string/obsolete/nsXPIDLString.cpp
+++ b/mozilla/xpcom/string/obsolete/nsXPIDLString.cpp
@@ -128,7 +128,8 @@ nsXPIDLCString& nsXPIDLCString::operator =(const char* aCString)
     if (mBufOwner && mBuf)
         XPIDL_FREE(mBuf);
 	
-    mBuf = Copy(aCString);
+    if (aCString)
+        mBuf = Copy(aCString);
     mBufOwner = PR_TRUE;
     
     return *this;