matplotlib · rcomer · Jan 24, 2023 · Jan 24, 2023
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -5748,9 +5748,10 @@ def _pcolorargs(self, funcname, *args, shading='auto', **kwargs):
 
         if shading == 'flat':
             if (Nx, Ny) != (ncols + 1, nrows + 1):
-                raise TypeError('Dimensions of C %s are incompatible with'
-                                ' X (%d) and/or Y (%d); see help(%s)' % (
-                                    C.shape, Nx, Ny, funcname))
+                raise TypeError(f"Dimensions of C {C.shape} should"
+                                f" be one smaller than X({Nx}) and Y({Ny})"
+                                f" while using shading='flat'"
+                                f" see help({funcname})")
         else:    # ['nearest', 'gouraud']:
             if (Nx, Ny) != (ncols, nrows):
                 raise TypeError('Dimensions of C %s are incompatible with'

diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -1439,6 +1439,14 @@ def test_pcolorflaterror():
         ax.pcolormesh(x, y, Z, shading='flat')
 
 
+def test_samesizepcolorflaterror():
+    fig, ax = plt.subplots()
+    x, y = np.meshgrid(np.arange(5), np.arange(3))
+    Z = x + y
+    with pytest.raises(TypeError, match=r".*one smaller than X"):
+        ax.pcolormesh(x, y, Z, shading='flat')
+
+
 @pytest.mark.parametrize('snap', [False, True])
 @check_figures_equal(extensions=["png"])
 def test_pcolorauto(fig_test, fig_ref, snap):