diff --git a/netwerk/mime/nsMIMEHeaderParamImpl.cpp b/netwerk/mime/nsMIMEHeaderParamImpl.cpp
index 4bc5414a648..8490f63a1cb 100644
--- a/netwerk/mime/nsMIMEHeaderParamImpl.cpp
+++ b/netwerk/mime/nsMIMEHeaderParamImpl.cpp
@@ -619,7 +619,13 @@ nsMIMEHeaderParamImpl::DoParameterInternal(const char *aHeaderValue,
     //   skip over whitespace, ';', whitespace.
 increment_str:      
     while (nsCRT::IsAsciiSpace(*str)) ++str;
-    if (*str == ';') ++str;
+    if (*str == ';') {
+      ++str;
+    } else {
+      // stop processing the header field; either we are done or the
+      // separator was missing
+      break;
+    }
     while (nsCRT::IsAsciiSpace(*str)) ++str;
   }
 
diff --git a/netwerk/test/unit/test_MIME_params.js b/netwerk/test/unit/test_MIME_params.js
index 8fee955b6b6..22e63730c5e 100644
--- a/netwerk/test/unit/test_MIME_params.js
+++ b/netwerk/test/unit/test_MIME_params.js
@@ -112,7 +112,7 @@ var tests = [
 
   // First series, only please, and don't slurp up higher elements (*2 in this
   // case) from later series into earlier one (invalid; error recovery)
-  ["attachment; filename=basic; filename*0*=UTF-8''multi\r\n"
+  ["attachment; filename=basic; filename*0*=UTF-8''multi;\r\n"
     + " filename*1=line;\r\n" 
     + " filename*0*=UTF-8''wrong;\r\n"
     + " filename*1=bad;\r\n"
@@ -397,9 +397,16 @@ var tests = [
    "attachment", "basic"],
 
   // Bug 732369: Content-Disposition parser does not require presence of ";" between params
+  // optimally, this would not even return the disposition type "attachment"  
 
   ["attachment; extension=bla filename=foo", 
+   "attachment", Cr.NS_ERROR_INVALID_ARG], 
+
+  ["attachment; filename=foo extension=bla", 
    "attachment", "foo"], 
+
+  ["attachment filename=foo", 
+   "attachment", Cr.NS_ERROR_INVALID_ARG], 
 ];
 
 var rfc5987paramtests = [