diff --git a/k-Wave/private/kspaceFirstOrder_inputChecking.m b/k-Wave/private/kspaceFirstOrder_inputChecking.m
index 20ebb6d..bc63619 100644
--- a/k-Wave/private/kspaceFirstOrder_inputChecking.m
+++ b/k-Wave/private/kspaceFirstOrder_inputChecking.m
@@ -213,7 +213,7 @@
         end
 
         % check y is real and within 0 to 3
-        if ~isreal(medium.alpha_coeff) || (medium.alpha_power >= 3 || medium.alpha_power < 0)
+        if ~isreal(medium.alpha_power) || (medium.alpha_power >= 3 || medium.alpha_power < 0)
             error('medium.alpha_power must be a real number between 0 and 3.');
         end