diff --git a/gprMax/cmds_geometry/add_grass.py b/gprMax/cmds_geometry/add_grass.py
index 04102295..8e3f969d 100644
--- a/gprMax/cmds_geometry/add_grass.py
+++ b/gprMax/cmds_geometry/add_grass.py
@@ -235,7 +235,7 @@ class AddGrass(UserObjectGeometry):
         surface.grass.append(g)
 
         # Check to see if grass has been already defined as a material
-        if all(x.ID == "grass" for x in grid.materials):
+        if not any(x.ID == "grass" for x in grid.materials):
             create_grass(grid)
 
         # Check if time step for model is suitable for using grass
diff --git a/gprMax/cmds_geometry/add_surface_water.py b/gprMax/cmds_geometry/add_surface_water.py
index 9b0c4cd9..5bef6478 100644
--- a/gprMax/cmds_geometry/add_surface_water.py
+++ b/gprMax/cmds_geometry/add_surface_water.py
@@ -156,7 +156,7 @@ class AddSurfaceWater(UserObjectGeometry):
             raise ValueError
 
         # Check to see if water has been already defined as a material
-        if all(x.ID != "water" for x in grid.materials):
+        if not any(x.ID != "water" for x in grid.materials):
             create_water(grid)
 
         # Check if time step for model is suitable for using water
diff --git a/gprMax/cmds_multiuse.py b/gprMax/cmds_multiuse.py
index 0ba36075..b5127cb6 100644
--- a/gprMax/cmds_multiuse.py
+++ b/gprMax/cmds_multiuse.py
@@ -385,7 +385,7 @@ class HertzianDipole(UserObjectMulti):
         p2 = uip.round_to_grid_static_point(p1)
 
         # Check if there is a waveformID in the waveforms list
-        if all(x.ID == waveform_id for x in grid.waveforms):
+        if not any(x.ID == waveform_id for x in grid.waveforms):
             logger.exception(f"{self.params_str()} there is no waveform " + f"with the identifier {waveform_id}.")
             raise ValueError
 
@@ -526,7 +526,7 @@ class MagneticDipole(UserObjectMulti):
         p2 = uip.round_to_grid_static_point(p1)
 
         # Check if there is a waveformID in the waveforms list
-        if all(x.ID == waveform_id for x in grid.waveforms):
+        if not any(x.ID == waveform_id for x in grid.waveforms):
             logger.exception(f"{self.params_str()} there is no waveform " + f"with the identifier {waveform_id}.")
             raise ValueError