diff --git a/src/client/providers/completionSource.ts b/src/client/providers/completionSource.ts
index 58a0a48ae835..d238b9c5636c 100644
--- a/src/client/providers/completionSource.ts
+++ b/src/client/providers/completionSource.ts
@@ -117,6 +117,10 @@ export class CompletionSource {
         const t = new Tokenizer();
         const tokens = t.Tokenize(text);
         const index = tokens.getItemContaining(document.offsetAt(position));
-        return index >= 0 && (tokens[index].TokenType === TokenType.String || tokens[index].TokenType === TokenType.Comment);
+        if (index >= 0) {
+            const token = tokens.getItemAt(index);
+            return token.type === TokenType.String || token.type === TokenType.Comment;
+        }
+        return false;
     }
 }
diff --git a/src/test/language/textRangeCollection.test.ts b/src/test/language/textRangeCollection.test.ts
index 32522e63c778..53e5ff4dc650 100644
--- a/src/test/language/textRangeCollection.test.ts
+++ b/src/test/language/textRangeCollection.test.ts
@@ -32,7 +32,7 @@ suite('Language.TextRangeCollection', () => {
         assert.equal(c.getItemAt(1).start, 4);
         assert.equal(c.getItemAt(1).length, 2);
     });
-    test('Contains position', async () => {
+    test('Contains position (simple)', async () => {
         const items: TextRange[] = [];
         items.push(new TextRange(2, 1));
         items.push(new TextRange(4, 2));
@@ -43,6 +43,37 @@ suite('Language.TextRangeCollection', () => {
             assert.equal(index, results[i]);
         }
     });
+    test('Contains position (adjoint)', async () => {
+        const items: TextRange[] = [];
+        items.push(new TextRange(2, 1));
+        items.push(new TextRange(3, 2));
+        const c = new TextRangeCollection(items);
+        const results = [-1, -1, 0, 1, 1, -1, -1];
+        for (let i = 0; i < results.length; i += 1) {
+            const index = c.getItemContaining(i);
+            assert.equal(index, results[i]);
+        }
+    });
+    test('Contains position (out of range)', async () => {
+        const items: TextRange[] = [];
+        items.push(new TextRange(2, 1));
+        items.push(new TextRange(4, 2));
+        const c = new TextRangeCollection(items);
+        const positions = [-100, -1, 10, 100];
+        for (const p of positions) {
+            const index = c.getItemContaining(p);
+            assert.equal(index, -1);
+        }
+    });
+    test('Contains position (empty)', async () => {
+        const items: TextRange[] = [];
+        const c = new TextRangeCollection(items);
+        const positions = [-2, -1, 0, 1, 2, 3];
+        for (const p of positions) {
+            const index = c.getItemContaining(p);
+            assert.equal(index, -1);
+        }
+    });
     test('Item at position', async () => {
         const items: TextRange[] = [];
         items.push(new TextRange(2, 1));
diff --git a/src/test/language/tokenizer.test.ts b/src/test/language/tokenizer.test.ts
index 7642b88acfaa..cef3b08e5fb1 100644
--- a/src/test/language/tokenizer.test.ts
+++ b/src/test/language/tokenizer.test.ts
@@ -16,7 +16,7 @@ suite('Language.Tokenizer', () => {
         assert.equal(tokens.count, 0);
         assert.equal(tokens.length, 0);
     });
-    test('Strings', async () => {
+    test('Strings: unclosed', async () => {
         const t = new Tokenizer();
         const tokens = t.Tokenize(' "string" """line1\n#line2"""\t\'un#closed');
         assert.equal(tokens.count, 3);
@@ -28,6 +28,42 @@ suite('Language.Tokenizer', () => {
             assert.equal(tokens.getItemAt(i).type, TokenType.String);
         }
     });
+    test('Strings: block next to regular, double-quoted', async () => {
+        const t = new Tokenizer();
+        const tokens = t.Tokenize('"string""""s2"""');
+        assert.equal(tokens.count, 2);
+
+        const ranges = [0, 8, 8, 8];
+        for (let i = 0; i < tokens.count; i += 1) {
+            assert.equal(tokens.getItemAt(i).start, ranges[2 * i]);
+            assert.equal(tokens.getItemAt(i).length, ranges[2 * i + 1]);
+            assert.equal(tokens.getItemAt(i).type, TokenType.String);
+        }
+    });
+    test('Strings: block next to block, double-quoted', async () => {
+        const t = new Tokenizer();
+        const tokens = t.Tokenize('""""""""');
+        assert.equal(tokens.count, 2);
+
+        const ranges = [0, 6, 6, 2];
+        for (let i = 0; i < tokens.count; i += 1) {
+            assert.equal(tokens.getItemAt(i).start, ranges[2 * i]);
+            assert.equal(tokens.getItemAt(i).length, ranges[2 * i + 1]);
+            assert.equal(tokens.getItemAt(i).type, TokenType.String);
+        }
+    });
+    test('Strings: unclosed sequence of quotes', async () => {
+        const t = new Tokenizer();
+        const tokens = t.Tokenize('"""""');
+        assert.equal(tokens.count, 1);
+
+        const ranges = [0, 5];
+        for (let i = 0; i < tokens.count; i += 1) {
+            assert.equal(tokens.getItemAt(i).start, ranges[2 * i]);
+            assert.equal(tokens.getItemAt(i).length, ranges[2 * i + 1]);
+            assert.equal(tokens.getItemAt(i).type, TokenType.String);
+        }
+    });
     test('Comments', async () => {
         const t = new Tokenizer();
         const tokens = t.Tokenize(' #co"""mment1\n\t\n#comm\'ent2 ');