diff --git a/include/mbgl/style/function/camera_function.hpp b/include/mbgl/style/function/camera_function.hpp
index 2e4aac223..1b03cc8cf 100644
--- a/include/mbgl/style/function/camera_function.hpp
+++ b/include/mbgl/style/function/camera_function.hpp
@@ -25,7 +25,7 @@ public:
 
     T evaluate(float zoom) const {
         return stops.match([&] (const auto& s) {
-            return s.evaluate(Value(double(zoom))).value_or(T());
+            return s.evaluate(zoom).value_or(T());
         });
     }
     
diff --git a/include/mbgl/style/function/exponential_stops.hpp b/include/mbgl/style/function/exponential_stops.hpp
index 051f5aa9a..1c57ec6f5 100644
--- a/include/mbgl/style/function/exponential_stops.hpp
+++ b/include/mbgl/style/function/exponential_stops.hpp
@@ -22,28 +22,31 @@ public:
           base(base_) {
     }
 
-    optional<T> evaluate(const Value& value) const {
+    optional<T> evaluate(float z) const {
         if (stops.empty()) {
             assert(false);
             return T();
         }
 
-        optional<float> z = numericValue<float>(value);
-        if (!z) {
-            return T();
-        }
-
-        auto it = stops.upper_bound(*z);
+        auto it = stops.upper_bound(z);
         if (it == stops.end()) {
             return stops.rbegin()->second;
         } else if (it == stops.begin()) {
             return stops.begin()->second;
         } else {
             return util::interpolate(std::prev(it)->second, it->second,
-                util::interpolationFactor(base, { std::prev(it)->first, it->first }, *z));
+                util::interpolationFactor(base, { std::prev(it)->first, it->first }, z));
         }
     }
 
+    optional<T> evaluate(const Value& value) const {
+        optional<float> z = numericValue<float>(value);
+        if (!z) {
+            return T();
+        }
+        return evaluate(*z);
+    }
+
     friend bool operator==(const ExponentialStops& lhs,
                            const ExponentialStops& rhs) {
         return lhs.stops == rhs.stops && lhs.base == rhs.base;
diff --git a/include/mbgl/style/function/interval_stops.hpp b/include/mbgl/style/function/interval_stops.hpp
index 50f2b4845..a482a6081 100644
--- a/include/mbgl/style/function/interval_stops.hpp
+++ b/include/mbgl/style/function/interval_stops.hpp
@@ -18,18 +18,13 @@ public:
         : stops(std::move(stops_)) {
     }
 
-    optional<T> evaluate(const Value& value) const {
+    optional<T> evaluate(float z) const {
         if (stops.empty()) {
             assert(false);
             return {};
         }
 
-        optional<float> z = numericValue<float>(value);
-        if (!z) {
-            return {};
-        }
-
-        auto it = stops.upper_bound(*z);
+        auto it = stops.upper_bound(z);
         if (it == stops.end()) {
             return stops.rbegin()->second;
         } else if (it == stops.begin()) {
@@ -39,6 +34,14 @@ public:
         }
     }
 
+    optional<T> evaluate(const Value& value) const {
+        optional<float> z = numericValue<float>(value);
+        if (!z) {
+            return {};
+        }
+        return evaluate(*z);
+    }
+
     friend bool operator==(const IntervalStops& lhs,
                            const IntervalStops& rhs) {
         return lhs.stops == rhs.stops;