diff --git a/Eigen/src/Core/MathFunctions.h b/Eigen/src/Core/MathFunctions.h
index 5b5ca46..f64116a 100644
--- a/Eigen/src/Core/MathFunctions.h
+++ b/Eigen/src/Core/MathFunctions.h
@@ -339,7 +339,7 @@
 };
 
 // Complex sqrt defined in MathFunctionsImpl.h.
-template<typename T> std::complex<T> complex_sqrt(const std::complex<T>& a_x);
+template<typename T> EIGEN_DEVICE_FUNC std::complex<T> complex_sqrt(const std::complex<T>& a_x);
 
 // MSVC incorrectly handles inf cases.
 #if EIGEN_COMP_MSVC > 0