diff --git a/math/quat.cpp b/math/quat.cpp
index ff9ddcc1460..9225059c4a1 100644
--- a/math/quat.cpp
+++ b/math/quat.cpp
@@ -73,7 +73,7 @@ Quaternion Quaternion::zAxis(const Angle &angle) {
 	return q;
 }
 
-Quaternion Quaternion::slerpQuat(const Quaternion& to, const float t) {
+Quaternion Quaternion::slerpQuat(const Quaternion& to, const float t) const {
 	Quaternion dst;
 	float scale0, scale1;
 	float flip = 1.0f;
diff --git a/math/quat.h b/math/quat.h
index f411fee623b..02e7f70f978 100644
--- a/math/quat.h
+++ b/math/quat.h
@@ -189,7 +189,7 @@ public:
 	 * @param t		factor to slerp by.
 	 * @return		the resulting quaternion.
 	 */
-	Quaternion slerpQuat(const Quaternion& to, const float t);
+	Quaternion slerpQuat(const Quaternion& to, const float t) const;
 
 	/**
 	 * Get the direction vector specified by col