diff --git a/gtsam_unstable/slam/AHRS.h b/gtsam_unstable/slam/AHRS.h
index 284fe2fc6..01c61704b 100644
--- a/gtsam_unstable/slam/AHRS.h
+++ b/gtsam_unstable/slam/AHRS.h
@@ -14,7 +14,7 @@
 
 namespace gtsam {
 
-Matrix cov(const Matrix& m);
+GTSAM_UNSTABLE_EXPORT Matrix cov(const Matrix& m);
 
 class GTSAM_UNSTABLE_EXPORT AHRS {