diff --git a/dlls/avifil32/avifile.c b/dlls/avifil32/avifile.c
index af0315d6c0..f5abc1ca89 100644
--- a/dlls/avifil32/avifile.c
+++ b/dlls/avifil32/avifile.c
@@ -1424,11 +1424,21 @@ static HRESULT AVIFILE_AddRecord(IAVIFileImpl *This)
   /* pre-conditions */
   assert(This != NULL && This->ppStreams[0] != NULL);
 
-  if (This->idxRecords == NULL || This->cbIdxRecords == 0) {
-    This->cbIdxRecords += 1024 * sizeof(AVIINDEXENTRY);
-    This->idxRecords = HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, This->cbIdxRecords);
-    if (This->idxRecords == NULL)
+  if (This->idxRecords == NULL || This->cbIdxRecords / sizeof(AVIINDEXENTRY) <= This->nIdxRecords) {
+    DWORD new_count = This->cbIdxRecords + 1024 * sizeof(AVIINDEXENTRY);
+    void *mem;
+    if (!This->idxRecords)
+      mem = HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, new_count);
+    else
+      mem = HeapReAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, This->idxRecords, new_count);
+    if (mem) {
+      This->cbIdxRecords = new_count;
+      This->idxRecords = mem;
+    } else {
+      HeapFree(GetProcessHeap(), 0, This->idxRecords);
+      This->idxRecords = NULL;
       return AVIERR_MEMORY;
+    }
   }
 
   assert(This->nIdxRecords < This->cbIdxRecords/sizeof(AVIINDEXENTRY));