diff --git a/polymani.pl b/polymani.pl
index 42c4699..875d2be 100644
--- a/polymani.pl
+++ b/polymani.pl
@@ -71,11 +71,15 @@ simpoly(P, S) :-
     resulting in a second polynomial. The two first arguments are assumed to
     be ground. The polynomial resulting from the sum is in simplified form.
 */
-scalepoly(P1, P2, S) :-
+scalepoly(P1, C, S) :-
     is_polynomial_valid_in_predicate(P1, "scalepoly"),
-    is_polynomial_valid_in_predicate(P2, "scalepoly"),
-    scale_polynomial(P1, P2, S),
+    is_number_in_predicate(C, "scalepoly"),
+    scale_polynomial(P1, C, S),
     !.
+%% Tests:
+%% ?- scalepoly(3*x*z+2*z, 4, S).
+%@ S = 12*x*z+8*z.
+%% ?- scalepoly(3*x*z+2*z, 2, S).
 
 /*
     addpoly/3 adds two polynomials as expressions resulting in a
@@ -102,7 +106,7 @@ is_polynomial_valid_in_predicate(P, _) :-
     polynomial(P),
     !.
 is_polynomial_valid_in_predicate(P, F) :-
-    %% Writes the polynomial and fails otherwise
+    %% Otherwise, write the polynomial and fails
     write("Invalid polynomial in "),
     write(F),
     write(": "),
@@ -133,6 +137,20 @@ is_polynomial_as_list_valid_in_predicate(L, F) :-
 %@ Invalid polynomial in Test: a*4+0*x
 %@ false.
 
+%% is_number_in_predicate(+C:number, +F:string) is det
+%
+%  Validates that C is a number or prints F and it then it
+%
+is_number_in_predicate(C, _) :-
+    number(C),
+    !.
+is_number_in_predicate(C, F) :-
+    %% Writes the argument and fails
+    write("Invalid number in "),
+    write(F),
+    write(": "),
+    write(C),
+    fail.
 
                  /*******************************
                  *            BACKEND           *
@@ -775,6 +793,8 @@ polynomial_to_list(T, [T]) :-
 %@ S = [-2*y, 5, 2*x^2].
 %% ?- polynomial_to_list(2*x^2-5-y*2, S).
 %@ S = [-2*y, -5, 2*x^2].
+%% ?- polynomial_to_list(P, [-2*y, -5, 2*x^2]).
+%@ ERROR: Unhandled exception: type_error(_527068=_527074*_527076,2,'a real number',_527074*_527076)
 
 %% list_to_polynomial(+L:List, -P:Polynomial) is det
 %