diff --git a/internal/ceres/function_sample.h b/internal/ceres/function_sample.h
index df79aef..3bcea1b 100644
--- a/internal/ceres/function_sample.h
+++ b/internal/ceres/function_sample.h
@@ -32,7 +32,9 @@
 #define CERES_INTERNAL_FUNCTION_SAMPLE_H_
 
 #include <string>
+
 #include "ceres/internal/eigen.h"
+#include "ceres/internal/port.h"
 
 namespace ceres {
 namespace internal {
@@ -45,7 +47,7 @@
 // line/direction. FunctionSample contains the information in two
 // ways. Information in the ambient space and information along the
 // direction of search.
-struct FunctionSample {
+struct CERES_EXPORT_INTERNAL FunctionSample {
   FunctionSample();
   FunctionSample(double x, double value);
   FunctionSample(double x, double value, double gradient);
@@ -85,9 +87,6 @@
   bool gradient_is_valid;
 };
 
-
-
-
 }  // namespace internal
 }  // namespace ceres