diff --git a/tools/OILGen.cpp b/tools/OILGen.cpp
index 5fb2fbd..d2671ce 100644
--- a/tools/OILGen.cpp
+++ b/tools/OILGen.cpp
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#include <gflags/gflags.h>
 #include <glog/logging.h>
 
 #include <cstdlib>