diff --git a/openlayers3/openlayers3.d.ts b/openlayers3/openlayers3.d.ts
index 9f06166da..28050055d 100644
--- a/openlayers3/openlayers3.d.ts
+++ b/openlayers3/openlayers3.d.ts
@@ -2152,26 +2152,26 @@ declare module ol {
             /**
              * Set the style for features. This can be a single style object, an array of styles, or a function that takes a feature and resolution and returns an array of styles. If it is undefined the default style is used. If it is null the layer has no style (a null style), so only features that have their own styles will be rendered in the layer. See ol.style for information on the default style.
              */
-            setStyle();
+            setStyle(): void;
 
             /**
              * Set the style for features. This can be a single style object, an array of styles, or a function that takes a feature and resolution and returns an array of styles. If it is undefined the default style is used. If it is null the layer has no style (a null style), so only features that have their own styles will be rendered in the layer. See ol.style for information on the default style.
              * @param layer Layer style
              */
-            setStyle(style: ol.style.Style);
+            setStyle(style: ol.style.Style): void;
 
             /**
              * Set the style for features. This can be a single style object, an array of styles, or a function that takes a feature and resolution and returns an array of styles. If it is undefined the default style is used. If it is null the layer has no style (a null style), so only features that have their own styles will be rendered in the layer. See ol.style for information on the default style.
              * @param layer Layer style
              */
-            setStyle(style: Array<ol.style.Style>);
+            setStyle(style: Array<ol.style.Style>): void;
 
             /**
              * Set the style for features. This can be a single style object, an array of styles, or a function that takes a feature and resolution and returns an array of styles. If it is undefined the default style is used. If it is null the layer has no style (a null style), so only features that have their own styles will be rendered in the layer. See ol.style for information on the default style.
              * @param Layer style
              */
             // TODO: Replace 'any' with ol.style.StyleFunction
-            setStyle(style: any);
+            setStyle(style: any): void;
         }
 
         interface BaseOptions {