Fixes #86386

src/vs/workbench/contrib/snippets/browser/snippetCompletionProvider.ts

@@ -126,8 +126,9 @@ export class SnippetCompletionProvider implements CompletionItemProvider {
 				// add remaing snippets when the current prefix ends in whitespace or when no
 				// interesting positions have been found
 				availableSnippets.forEach(snippet => {
-					const range = Range.fromPositions(position);
-					suggestions.push(new SnippetCompletion(snippet, { replace: range, insert: range }));
+					let insert = Range.fromPositions(position);
+					let replace = startsWith(lineSuffixLow, snippet.prefixLow) ? insert.setEndPosition(position.lineNumber, position.column + snippet.prefixLow.length) : insert;
+					suggestions.push(new SnippetCompletion(snippet, { replace, insert }));
 				});
 			}
 

src/vs/workbench/contrib/snippets/test/browser/snippetsService.test.ts

@@ -438,5 +438,13 @@ suite('SnippetsService', function () {
 		[first] = result.suggestions;
 		assert.equal((first.range as any).insert.endColumn, 3);
 		assert.equal((first.range as any).replace.endColumn, 3);
+
+		model = TextModel.createFromString('not word', undefined, modeService.getLanguageIdentifier('fooLang'));
+		result = await provider.provideCompletionItems(model, new Position(1, 1), context)!;
+
+		assert.equal(result.suggestions.length, 1);
+		[first] = result.suggestions;
+		assert.equal((first.range as any).insert.endColumn, 1);
+		assert.equal((first.range as any).replace.endColumn, 9);
 	});
 });