diff --git a/src/vs/base/common/diff/diff.ts b/src/vs/base/common/diff/diff.ts
index 3fceba4c97414c0a1688fe24e91b7d717a87748c..7f98094c4bbdeef4764ede3d5b4bdcd39cc1a250 100644
--- a/src/vs/base/common/diff/diff.ts
+++ b/src/vs/base/common/diff/diff.ts
@@ -211,6 +211,8 @@ class DiffChangeHelper {
 
 }
 
+const hasOwnProperty = Object.prototype.hasOwnProperty;
+
 /**
  * An implementation of the difference algorithm described in
  * "An O(ND) Difference Algorithm and its letiations" by Eugene W. Myers
@@ -257,7 +259,7 @@ export class LcsDiff {
 		// Fill up the hash table for unique elements
 		for (i = 0; i < originalSequenceLength; i++) {
 			let originalElementHash = this.OriginalSequence.getElementHash(i);
-			if (!hashTable.hasOwnProperty(originalElementHash)) {
+			if (!hasOwnProperty.call(hashTable, originalElementHash)) {
 				// No entry in the hashtable so this is a new unique element.
 				// Assign the element a new unique identifier and add it to the
 				// hash table
@@ -271,7 +273,7 @@ export class LcsDiff {
 		// Now match up modified elements
 		for (i = 0; i < modifiedSequenceLength; i++) {
 			let modifiedElementHash = this.ModifiedSequence.getElementHash(i);
-			if (!hashTable.hasOwnProperty(modifiedElementHash)) {
+			if (!hasOwnProperty.call(hashTable, modifiedElementHash)) {
 				this.m_modifiedIds[i] = currentUniqueId++;
 				hashTable[modifiedElementHash] = this.m_modifiedIds[i];
 			} else {
diff --git a/src/vs/editor/test/common/diff/diffComputer.test.ts b/src/vs/editor/test/common/diff/diffComputer.test.ts
index fe8850102ad441aed202bd1921f31aad8c17f6e4..192bbc4e5c266a77ed4caec256f8beee1d858a5c 100644
--- a/src/vs/editor/test/common/diff/diffComputer.test.ts
+++ b/src/vs/editor/test/common/diff/diffComputer.test.ts
@@ -394,4 +394,13 @@ suite('Editor Diff - DiffComputer', () => {
 		];
 		assertDiff(original, modified, expected, false, true);
 	});
+
+	test('issue #12122 r.hasOwnProperty is not a function', () => {
+		var original = [ 'hasOwnProperty' ];
+		var modified = [ 'hasOwnProperty', 'and another line' ];
+		var expected = [
+			createLineInsertion(2, 2, 1)
+		];
+		assertDiff(original, modified, expected);
+	});
 });