diff --git a/src/services/completions.ts b/src/services/completions.ts
index 1c3288a3282..35f03697dd0 100644
--- a/src/services/completions.ts
+++ b/src/services/completions.ts
@@ -1000,6 +1000,7 @@ namespace ts.Completions {
         let completionKind = CompletionKind.None;
         let isNewIdentifierLocation = false;
         let keywordFilters = KeywordCompletionFilters.None;
+        // This also gets mutated in nested-functions after the return
         let symbols: Symbol[] = [];
         const symbolToOriginInfoMap: SymbolOriginInfoMap = [];
         const symbolToSortTextMap: SymbolSortTextMap = [];
@@ -1342,9 +1343,12 @@ namespace ts.Completions {
                     }
 
                     const symbolId = getSymbolId(symbol);
-                    symbols.push(symbol);
-                    symbolToOriginInfoMap[symbolId] = origin;
-                    symbolToSortTextMap[symbolId] = SortText.AutoImportSuggestions;
+                    const existingSymbol = findLast(symbols, symbol => symbol.id === symbolId);
+                    if (!existingSymbol) {
+                        symbols.push(symbol);
+                        symbolToOriginInfoMap[symbolId] = origin;
+                        symbolToSortTextMap[symbolId] = SortText.AutoImportSuggestions;
+                    }
                 });
             }
             filterGlobalCompletion(symbols);
diff --git a/tests/cases/fourslash/completionsRedeclareModuleAsGlobal.ts b/tests/cases/fourslash/completionsRedeclareModuleAsGlobal.ts
new file mode 100644
index 00000000000..4a17a0830ac
--- /dev/null
+++ b/tests/cases/fourslash/completionsRedeclareModuleAsGlobal.ts
@@ -0,0 +1,33 @@
+/// <reference path="fourslash.ts" />
+
+// @esModuleInterop: true,
+// @target: esnext
+
+// @Filename: /myAssert.d.ts
+////declare function assert(value:any, message?:string):void;
+////export = assert;
+////export as namespace assert;
+
+// @Filename: /ambient.d.ts
+////import assert from './myAssert';
+////
+////type Assert = typeof assert;
+////
+////declare global {
+////  const assert: Assert;
+////}
+
+// @Filename: /index.ts
+/////// <reference path="./ambient.d.ts" />
+////asser/**/;
+
+verify.completions({
+  marker: "",
+  includes: [
+    {
+      name: "assert",
+      sortText: completion.SortText.GlobalsOrKeywords
+    }
+  ],
+  preferences: { includeCompletionsForModuleExports: true, includeInsertTextCompletions: true }
+});