diff --git a/io/GDALGrid.hpp b/io/GDALGrid.hpp
index 0225f1a1aa..3500b94659 100644
--- a/io/GDALGrid.hpp
+++ b/io/GDALGrid.hpp
@@ -60,8 +60,9 @@ class GDALGrid
         {}
     };
 
-    GDALGrid(size_t width, size_t height, double edgeLength, double radius,
-        int outputTypes, size_t windowSize);
+    // Exported for testing.
+    PDAL_DLL GDALGrid(size_t width, size_t height,
+        double edgeLength, double radius, int outputTypes, size_t windowSize);
 
     void expand(size_t width, size_t height, size_t xshift, size_t yshift);