diff --git a/index.js b/index.js
index b5ffd50..ca7e30f 100644
--- a/index.js
+++ b/index.js
@@ -32,6 +32,7 @@ function createFunction(parameters, defaultType) {
                 var stop = parameters.stops[s];
                 if (featureFunctions[stop[0].zoom] === undefined) {
                     featureFunctions[stop[0].zoom] = {
+                        zoom: stop[0].zoom,
                         type: parameters.type,
                         property: parameters.property,
                         stops: []
@@ -41,7 +42,7 @@ function createFunction(parameters, defaultType) {
             }
 
             for (var z in featureFunctions) {
-                featureFunctionStops.push([parseInt(z), createFunction(featureFunctions[z])]);
+                featureFunctionStops.push([featureFunctions[z].zoom, createFunction(featureFunctions[z])]);
             }
             fun = function(zoom, feature) {
                 return evaluateExponentialFunction({ stops: featureFunctionStops, base: parameters.base }, zoom)(zoom, feature);
diff --git a/test/test.js b/test/test.js
index 9cf02b4..7989afa 100644
--- a/test/test.js
+++ b/test/test.js
@@ -176,6 +176,26 @@ test('function types', function(t) {
 
                 t.end();
             });
+
+            t.test('fractional zoom', function(t) {
+                var f = MapboxGLFunction({
+                    type: 'exponential',
+                    property: 'prop',
+                    base: 1,
+                    stops: [
+                        [{ zoom: 1.9, value: 0 }, 4],
+                        [{ zoom: 2.1, value: 0 }, 8]
+                    ]
+                });
+
+                t.equal(f(1.9, { prop: 1 }), 4);
+                t.equal(f(2, { prop: 1 }), 6);
+                t.equal(f(2.1, { prop: 1 }), 8);
+
+                t.end();
+            });
+
+
         });