diff --git a/CHANGELOG.MD b/CHANGELOG.MD
index b80fa60c..1b36ba48 100644
--- a/CHANGELOG.MD
+++ b/CHANGELOG.MD
@@ -1,5 +1,8 @@
 # Changelog
 
+### 15.1.1 (*2021-05-09*)
+- Fixed: `tooltips` option accepts one `Formatter` for all tooltips (#1101);
+
 ### 15.1.0 (*2021-05-09*)
 - Added: `drag` event when dragging connecting elements (#887, #1135);
 
diff --git a/package-lock.json b/package-lock.json
index b2d39293..397ba1cb 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "nouislider",
-  "version": "15.1.0",
+  "version": "15.1.1",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
diff --git a/package.json b/package.json
index 76f47ac5..528a0e02 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "nouislider",
-  "version": "15.1.0",
+  "version": "15.1.1",
   "main": "dist/nouislider.js",
   "style": "dist/nouislider.min.css",
   "types": "dist/nouislider.d.ts",
diff --git a/src/nouislider.ts b/src/nouislider.ts
index 4b38d215..bbdef1d9 100644
--- a/src/nouislider.ts
+++ b/src/nouislider.ts
@@ -276,8 +276,8 @@ type EventCallback = (
 
 //region Helper Methods
 
-function isValidFormatter(entry: Formatter): entry is Formatter {
-    return typeof entry === "object" && typeof entry.to === "function" && typeof entry.from === "function";
+function isValidFormatter(entry: unknown): entry is Formatter {
+    return typeof entry === "object" && typeof (<Formatter>entry).to === "function" && typeof (<Formatter>entry).from === "function";
 }
 
 function removeElement(el: HTMLElement): void {
@@ -1153,11 +1153,11 @@ function testTooltips(parsed: ParsedOptions, entry: boolean | Formatter | (boole
         return;
     }
 
-    if (entry === true) {
+    if (entry === true || isValidFormatter(entry)) {
         parsed.tooltips = [];
 
         for (let i = 0; i < parsed.handles; i++) {
-            parsed.tooltips.push(true);
+            parsed.tooltips.push(entry);
         }
     } else {
         entry = asArray(entry);