From 1b8b0602cba5a9a003563bfc21b1ba1c6ebd0cad Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Tue, 18 May 2021 16:37:26 -0400
Subject: [PATCH] Backport PR #20248: Replace pgf image-streaming warning by
 error.

---
 lib/matplotlib/backends/backend_pgf.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/matplotlib/backends/backend_pgf.py b/lib/matplotlib/backends/backend_pgf.py
index 9d01f603e021..355090608c0c 100644
--- a/lib/matplotlib/backends/backend_pgf.py
+++ b/lib/matplotlib/backends/backend_pgf.py
@@ -635,9 +635,9 @@ def draw_image(self, gc, x, y, im, transform=None):
             return
 
         if not os.path.exists(getattr(self.fh, "name", "")):
-            _api.warn_external(
+            raise ValueError(
                 "streamed pgf-code does not support raster graphics, consider "
-                "using the pgf-to-pdf option.")
+                "using the pgf-to-pdf option")
 
         # save the images to png files
         path = pathlib.Path(self.fh.name)