--- a/netwerk/mime/nsMIMEHeaderParamImpl.cpp
+++ b/netwerk/mime/nsMIMEHeaderParamImpl.cpp
@@ -447,17 +447,17 @@ nsMIMEHeaderParamImpl::DoParameterIntern
 
   int32_t paramLen = strlen(aParamName);
 
   while (*str) {
     // find name/value
 
     const char *nameStart = str;
     const char *nameEnd = nullptr;
-    const char *valueStart = str;
+    const char *valueStart = nullptr;
     const char *valueEnd = nullptr;
     bool isQuotedString = false;
 
     NS_ASSERTION(!nsCRT::IsAsciiSpace(*str), "should be after whitespace.");
 
     // Skip forward to the end of this token.
     for (; *str && !nsCRT::IsAsciiSpace(*str) && *str != '=' && *str != ';'; str++)
       ;