diff --git a/web/ui/module/codemirror-promql/src/complete/hybrid.test.ts b/web/ui/module/codemirror-promql/src/complete/hybrid.test.ts
index 8250319681..5906a692de 100644
--- a/web/ui/module/codemirror-promql/src/complete/hybrid.test.ts
+++ b/web/ui/module/codemirror-promql/src/complete/hybrid.test.ts
@@ -922,6 +922,30 @@ describe('computeEndCompletePosition test', () => {
       pos: 12, // cursor after '{'
       expectedEnd: 12,
     },
+    {
+      title: 'cursor in middle of label name in grouping clause - should extend to end',
+      expr: 'sum by (instance_name)',
+      pos: 12, // cursor after 'inst' (before 'ance')
+      expectedEnd: 21, // should extend to end of 'instance_name'
+    },
+    {
+      title: 'cursor in middle of label name in label matcher - should extend to end',
+      expr: 'metric{instance_name="value"}',
+      pos: 11, // cursor after 'inst' (before 'ance')
+      expectedEnd: 20, // should extend to end of 'instance_name'
+    },
+    {
+      title: 'cursor in middle of label name in on() modifier - should extend to end',
+      expr: 'a / on(instance_name) b',
+      pos: 11, // cursor after 'inst' (before 'ance')
+      expectedEnd: 20, // should extend to end of 'instance_name'
+    },
+    {
+      title: 'cursor in middle of label name in ignoring() modifier - should extend to end',
+      expr: 'a / ignoring(instance_name) b',
+      pos: 17, // cursor after 'inst' (before 'ance')
+      expectedEnd: 26, // should extend to end of 'instance_name'
+    },
   ];
   testCases.forEach((value) => {
     it(value.title, () => {
diff --git a/web/ui/module/codemirror-promql/src/complete/hybrid.ts b/web/ui/module/codemirror-promql/src/complete/hybrid.ts
index d89907699a..23e47ce649 100644
--- a/web/ui/module/codemirror-promql/src/complete/hybrid.ts
+++ b/web/ui/module/codemirror-promql/src/complete/hybrid.ts
@@ -167,13 +167,14 @@ function arrayToCompletionResult(data: Completion[], from: number, to: number, i
 }
 
 // computeEndCompletePosition calculates the end position for autocompletion replacement.
-// When the cursor is in the middle of an identifier (e.g., metric name), this ensures the entire
-// identifier is replaced, not just the portion before the cursor. This fixes issue #15839.
+// When the cursor is in the middle of an identifier (e.g., metric name) or label name, this ensures
+// the entire token is replaced, not just the portion before the cursor. This fixes issue #15839.
 // Note: this method is exported only for testing purpose.
 export function computeEndCompletePosition(state: EditorState, node: SyntaxNode, pos: number): number {
-  // For Identifier nodes (metric names), extend the end position to include
-  // the entire identifier, even if the cursor is in the middle.
-  if (node.type.id === Identifier) {
+  // For Identifier nodes (metric names) and LabelName nodes (label names in matchers,
+  // grouping clauses, etc.), extend the end position to include the entire token,
+  // even if the cursor is in the middle.
+  if (node.type.id === Identifier || node.type.id === LabelName) {
     return node.to;
   }
   // Default: use the cursor position as the end position