diff --git a/arch/arm/boot/dts/r8a7791-koelsch.dts b/arch/arm/boot/dts/r8a7791-koelsch.dts
index d431f3189bba..fd556c3483e3 100644
--- a/arch/arm/boot/dts/r8a7791-koelsch.dts
+++ b/arch/arm/boot/dts/r8a7791-koelsch.dts
@@ -45,6 +45,10 @@
 	};
 };
 
+&extal_clk {
+	clock-frequency = <20000000>;
+};
+
 &pfc {
 	pinctrl-0 = <&scif0_pins &scif1_pins>;
 	pinctrl-names = "default";