diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
index 6fdf1265ff3b..b8b91e9a0dd4 100644
--- a/lib/matplotlib/figure.py
+++ b/lib/matplotlib/figure.py
@@ -1471,6 +1471,9 @@ def subplots(self, nrows=1, ncols=1, sharex=False, sharey=False,
             subplot_kw = {}
         if gridspec_kw is None:
             gridspec_kw = {}
+        # don't mutate kwargs passed by user...
+        subplot_kw = subplot_kw.copy()
+        gridspec_kw = gridspec_kw.copy()
 
         if self.get_constrained_layout():
             gs = GridSpec(nrows, ncols, figure=self, **gridspec_kw)
diff --git a/lib/matplotlib/tests/test_subplots.py b/lib/matplotlib/tests/test_subplots.py
index 30cebe656e58..8c3558d10ca5 100644
--- a/lib/matplotlib/tests/test_subplots.py
+++ b/lib/matplotlib/tests/test_subplots.py
@@ -149,3 +149,12 @@ def test_get_gridspec():
     # ahem, pretty trivial, but...
     fig, ax = plt.subplots()
     assert ax.get_subplotspec().get_gridspec() == ax.get_gridspec()
+
+
+def test_dont_mutate_kwargs():
+    subplot_kw = {'sharex': 'all'}
+    gridspec_kw = {'width_ratios': [1, 2]}
+    fig, ax = plt.subplots(1, 2, subplot_kw=subplot_kw,
+                           gridspec_kw=gridspec_kw)
+    assert subplot_kw == {'sharex': 'all'}
+    assert gridspec_kw == {'width_ratios': [1, 2]}