diff --git a/mozilla/string/obsolete/nsString2.cpp b/mozilla/string/obsolete/nsString2.cpp
index 1e85b47def2..e65897a989c 100644
--- a/mozilla/string/obsolete/nsString2.cpp
+++ b/mozilla/string/obsolete/nsString2.cpp
@@ -784,7 +784,7 @@ char* nsString::ToCString(char* aBuf, PRUint32 aBufLength,PRUint32 anOffset) con
 
     CBufDescriptor theDescr(aBuf,PR_TRUE,aBufLength,0);
     nsCAutoString temp(theDescr);
-    nsStr::StrAssign(temp, *this, anOffset, aBufLength-1);
+    nsStr::StrAssign(temp, *this, anOffset, PR_MIN(mLength, aBufLength-1));
     temp.mStr=0;
   }
   return aBuf;
diff --git a/mozilla/xpcom/ds/nsString2.cpp b/mozilla/xpcom/ds/nsString2.cpp
index 1e85b47def2..e65897a989c 100644
--- a/mozilla/xpcom/ds/nsString2.cpp
+++ b/mozilla/xpcom/ds/nsString2.cpp
@@ -784,7 +784,7 @@ char* nsString::ToCString(char* aBuf, PRUint32 aBufLength,PRUint32 anOffset) con
 
     CBufDescriptor theDescr(aBuf,PR_TRUE,aBufLength,0);
     nsCAutoString temp(theDescr);
-    nsStr::StrAssign(temp, *this, anOffset, aBufLength-1);
+    nsStr::StrAssign(temp, *this, anOffset, PR_MIN(mLength, aBufLength-1));
     temp.mStr=0;
   }
   return aBuf;
diff --git a/mozilla/xpcom/string/obsolete/nsString2.cpp b/mozilla/xpcom/string/obsolete/nsString2.cpp
index 1e85b47def2..e65897a989c 100644
--- a/mozilla/xpcom/string/obsolete/nsString2.cpp
+++ b/mozilla/xpcom/string/obsolete/nsString2.cpp
@@ -784,7 +784,7 @@ char* nsString::ToCString(char* aBuf, PRUint32 aBufLength,PRUint32 anOffset) con
 
     CBufDescriptor theDescr(aBuf,PR_TRUE,aBufLength,0);
     nsCAutoString temp(theDescr);
-    nsStr::StrAssign(temp, *this, anOffset, aBufLength-1);
+    nsStr::StrAssign(temp, *this, anOffset, PR_MIN(mLength, aBufLength-1));
     temp.mStr=0;
   }
   return aBuf;