diff --git a/.circleci/config.yml b/.circleci/config.yml
@@ -141,14 +141,32 @@ commands:
                [ "$CIRCLE_PR_NUMBER" = "" ]; then
               export RELEASE_TAG='-t release'
             fi
-            make html O="-T $RELEASE_TAG -j4"
+            make html O="-T $RELEASE_TAG -j4 -w /tmp/sphinxerrorswarnings.log"
             rm -r build/html/_sources
           working_directory: doc
       - save_cache:
           key: sphinx-env-v1-{{ .BuildNum }}-{{ .Environment.CIRCLE_JOB }}
           paths:
             - doc/build/doctrees
 
+  doc-show-errors-warnings:
+    steps:
+      - run:
+          name: Extract possible build errors and warnings
+          command: |
+           (grep "WARNING\|ERROR" /tmp/sphinxerrorswarnings.log ||
+            echo "No errors or warnings")
+
+  doc-show-deprecations:
+    steps:
+      - run:
+          name: Extract possible deprecation warnings in examples and tutorials
+          command: |
+           (grep DeprecationWarning -r -l doc/build/html/gallery ||
+            echo "No deprecation warnings in gallery")
+           (grep DeprecationWarning -r -l doc/build/html/tutorials ||
+            echo "No deprecation warnings in tutorials")
+
   doc-bundle:
     steps:
       - run:
@@ -186,6 +204,8 @@ jobs:
       - doc-deps-install
 
       - doc-build
+      - doc-show-errors-warnings
+      - doc-show-deprecations
 
       - doc-bundle
 

diff --git a/examples/images_contours_and_fields/pcolormesh_grids.py b/examples/images_contours_and_fields/pcolormesh_grids.py
@@ -54,11 +54,10 @@ def _annotate(ax, x, y, title):
 # -----------------------------
 #
 # Often, however, data is provided where *X* and *Y* match the shape of *Z*.
-# While this makes sense for other ``shading`` types, it is no longer permitted
-# when ``shading='flat'`` (and will raise a MatplotlibDeprecationWarning as of
-# Matplotlib v3.3). Historically, Matplotlib silently dropped the last row and
-# column of *Z* in this case, to match Matlab's behavior. If this behavior is
-# still desired, simply drop the last row and column manually:
+# While this makes sense for other ``shading`` types, it is not permitted
+# when ``shading='flat'``. Historically, Matplotlib silently dropped the last
+# row and column of *Z* in this case, to match Matlab's behavior. If this
+# behavior is still desired, simply drop the last row and column manually:
 
 x = np.arange(ncols)  # note *not* ncols + 1 as before
 y = np.arange(nrows)

diff --git a/examples/images_contours_and_fields/pcolormesh_levels.py b/examples/images_contours_and_fields/pcolormesh_levels.py
@@ -52,9 +52,8 @@
 # Often a user wants to pass *X* and *Y* with the same sizes as *Z* to
 # `.axes.Axes.pcolormesh`. This is also allowed if ``shading='auto'`` is
 # passed (default set by :rc:`pcolor.shading`). Pre Matplotlib 3.3,
-# ``shading='flat'`` would drop the last column and row of *Z*; while that
-# is still allowed for back compatibility purposes, a DeprecationWarning is
-# raised. If this is really what you want, then simply drop the last row and
+# ``shading='flat'`` would drop the last column and row of *Z*, but now gives
+# an error. If this is really what you want, then simply drop the last row and
 # column of Z manually:
 
 x = np.arange(10)  # len = 10