diff --git a/amount.go b/amount.go
index a15b311..e3d6de2 100644
--- a/amount.go
+++ b/amount.go
@@ -360,7 +360,10 @@ func (a Amount) Value() (driver.Value, error) {
 // Allows scanning amounts from a PostgreSQL composite type.
 func (a *Amount) Scan(src interface{}) error {
 	// Wire format: "(9.99,USD)".
-	input := src.(string)
+	input, ok := src.(string)
+	if !ok {
+		return fmt.Errorf("invalid src: %v", src)
+	}
 	if len(input) == 0 {
 		return nil
 	}