diff --git a/Sources/Units/Units.swift b/Sources/Units/Units.swift
index 56c3b74..2f42d72 100644
--- a/Sources/Units/Units.swift
+++ b/Sources/Units/Units.swift
@@ -414,12 +414,9 @@ public struct UnitValue<ValueType: ConvertibleToDouble>:
 
 	public func operation(
 		value: any ConvertibleToDouble,
-		op: (
-			_ lhs:
-				any ConvertibleToDouble, _ rhs: any ConvertibleToDouble
-		) -> any ConvertibleToDouble
+		op: (_ lhs: Double, _ rhs: Double) -> Double
 	) -> UnitValue<Double> {
-		op(self.value, value).doubleValue[self.unit]
+		op(self.value, value.doubleValue).doubleValue[self.unit]
 	}
 
 	// MARK: - Subscripts for UnitValue