diff --git a/widget/gtk/nsClipboard.cpp b/widget/gtk/nsClipboard.cpp
index bc9897b30ab9..5586eff96840 100644
--- a/widget/gtk/nsClipboard.cpp
+++ b/widget/gtk/nsClipboard.cpp
@@ -570,13 +570,14 @@ nsClipboard::SelectionGetEvent(GtkClipboard     *aClipboard,
     }
 
     void *primitive_data = nullptr;
+    uint32_t dataLen = 0;
     nsPrimitiveHelpers::CreateDataFromPrimitive(nsDependentCString(target_name),
-                                                item, &primitive_data, len);
+                                                item, &primitive_data, &dataLen);
 
     if (primitive_data) {
         gtk_selection_data_set(aSelectionData, selectionTarget,
                                8, /* 8 bits in a unit */
-                               (const guchar *)primitive_data, len);
+                               (const guchar *)primitive_data, dataLen);
         free(primitive_data);
     }
 
diff --git a/widget/gtk/nsDragService.cpp b/widget/gtk/nsDragService.cpp
index 820243339c6a..e8405fbf7b1e 100644
--- a/widget/gtk/nsDragService.cpp
+++ b/widget/gtk/nsDragService.cpp
@@ -1675,14 +1675,12 @@ nsDragService::SourceDataGet(GtkWidget        *aWidget,
         } else {
             actualFlavor = mimeFlavor.get();
         }
-
-        uint32_t tmpDataLen = 0;
-        void    *tmpData = nullptr;
         nsresult rv;
         nsCOMPtr<nsISupports> data;
+        uint32_t len;
         rv = item->GetTransferData(actualFlavor,
                                    getter_AddRefs(data),
-                                   &tmpDataLen);
+                                   &len);
 
         if (strcmp(actualFlavor, kFilePromiseMime) == 0) {
             if (NS_SUCCEEDED(rv)) {
@@ -1694,8 +1692,10 @@ nsDragService::SourceDataGet(GtkWidget        *aWidget,
         }
 
         if (NS_SUCCEEDED(rv)) {
+            void *tmpData = nullptr;
+            uint32_t tmpDataLen = 0;
             nsPrimitiveHelpers::CreateDataFromPrimitive(
-                nsDependentCString(actualFlavor), data, &tmpData, tmpDataLen);
+                nsDependentCString(actualFlavor), data, &tmpData, &tmpDataLen);
             // if required, do the extra work to convert unicode to plain
             // text and replace the output values with the plain text.
             if (needToDoConversionToPlainText) {
diff --git a/widget/nsPrimitiveHelpers.cpp b/widget/nsPrimitiveHelpers.cpp
index f98ead28d6a6..2157621e06bc 100644
--- a/widget/nsPrimitiveHelpers.cpp
+++ b/widget/nsPrimitiveHelpers.cpp
@@ -125,13 +125,14 @@ nsPrimitiveHelpers :: CreatePrimitiveForCFHTML ( const void* aDataBuff,
 // parameter does not reflect that.
 //
 void
-nsPrimitiveHelpers :: CreateDataFromPrimitive ( const nsACString& aFlavor, nsISupports* aPrimitive,
-                                                   void** aDataBuff, uint32_t aDataLen )
+nsPrimitiveHelpers::CreateDataFromPrimitive(const nsACString& aFlavor, nsISupports* aPrimitive,
+                                            void** aDataBuff, uint32_t*  aDataLen)
 {
   if ( !aDataBuff )
     return;
 
   *aDataBuff = nullptr;
+  *aDataLen = 0;
 
   if (aFlavor.EqualsLiteral(kTextMime) ||
       aFlavor.EqualsLiteral(kCustomTypesMime)) {
@@ -140,6 +141,7 @@ nsPrimitiveHelpers :: CreateDataFromPrimitive ( const nsACString& aFlavor, nsISu
       nsAutoCString data;
       plainText->GetData ( data );
       *aDataBuff = ToNewCString(data);
+      *aDataLen = data.Length() * sizeof(char);
     }
   }
   else {
@@ -148,6 +150,7 @@ nsPrimitiveHelpers :: CreateDataFromPrimitive ( const nsACString& aFlavor, nsISu
       nsAutoString data;
       doubleByteText->GetData ( data );
       *aDataBuff = ToNewUnicode(data);
+      *aDataLen = data.Length() * sizeof(char16_t);
     }
   }
 
diff --git a/widget/nsPrimitiveHelpers.h b/widget/nsPrimitiveHelpers.h
index 4a1455b07f58..7d8cbf6a3029 100644
--- a/widget/nsPrimitiveHelpers.h
+++ b/widget/nsPrimitiveHelpers.h
@@ -31,8 +31,8 @@ public:
     // Given a nsISupports* primitive and the flavor it represents, creates a new data
     // buffer with the data in it. This data will be null terminated, but the length
     // parameter does not reflect that.
-  static void CreateDataFromPrimitive ( const nsACString& aFlavor, nsISupports* aPrimitive, 
-                                         void** aDataBuff, uint32_t aDataLen ) ;
+  static void CreateDataFromPrimitive(const nsACString& aFlavor, nsISupports* aPrimitive,
+                                      void** aDataBuff, uint32_t* aDataLen);
 
 }; // class nsPrimitiveHelpers
 
diff --git a/widget/nsTransferable.cpp b/widget/nsTransferable.cpp
index b8822155cbe7..c67923d98500 100644
--- a/widget/nsTransferable.cpp
+++ b/widget/nsTransferable.cpp
@@ -126,9 +126,10 @@ DataStruct::WriteCache(nsISupports* aData, uint32_t aDataLen)
 
   // write out the contents of the clipboard to the file
   void* buff = nullptr;
-  nsPrimitiveHelpers::CreateDataFromPrimitive(mFlavor, aData, &buff, aDataLen);
+  uint32_t dataLen = 0;
+  nsPrimitiveHelpers::CreateDataFromPrimitive(mFlavor, aData, &buff, &dataLen);
   if (buff) {
-    int32_t written = PR_Write(mCacheFD, buff, aDataLen);
+    int32_t written = PR_Write(mCacheFD, buff, dataLen);
     free(buff);
     if (written) {
       return NS_OK;
diff --git a/widget/windows/nsDataObj.cpp b/widget/windows/nsDataObj.cpp
index 555f4d5c2efe..a0238d8b6fbe 100644
--- a/widget/windows/nsDataObj.cpp
+++ b/widget/windows/nsDataObj.cpp
@@ -1339,7 +1339,7 @@ HRESULT nsDataObj::GetText(const nsACString & aDataFlavor, FORMATETC& aFE, STGME
   if ( !len )
     return E_FAIL;
   nsPrimitiveHelpers::CreateDataFromPrimitive(
-    nsDependentCString(flavorStr), genericDataWrapper, &data, len);
+    nsDependentCString(flavorStr), genericDataWrapper, &data, &len);
   if ( !data )
     return E_FAIL;