diff --git a/lib/matplotlib/tests/baseline_images/test_axes/polar_axes.pdf b/lib/matplotlib/tests/baseline_images/test_axes/polar_axes.pdf
index bb3e921a0569..9847473382b4 100644
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diff --git a/lib/matplotlib/tests/baseline_images/test_axes/polar_axes.png b/lib/matplotlib/tests/baseline_images/test_axes/polar_axes.png
index a8b5499cf7de..a6e30e908857 100644
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index 3dc142f54a94..e348a3856db1 100644
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+++ b/lib/matplotlib/tests/baseline_images/test_axes/polar_axes.svg
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@@ -424,8 +429,8 @@ z
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@@ -532,8 +537,8 @@ z
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diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
index 194bcf9ba06f..4da7f124241d 100644
--- a/lib/matplotlib/tests/test_axes.py
+++ b/lib/matplotlib/tests/test_axes.py
@@ -129,6 +129,7 @@ def test_polar_annotations():
     fig = plt.figure()
     ax = fig.add_subplot( 111, polar=True )
     line, = ax.plot( theta, r, color='#ee8d18', lw=3 )
+    line, = ax.plot( (0, 0), (0, 1), color="#0000ff", lw=1)
 
     ind = 800
     thisr, thistheta = r[ind], theta[ind]
diff --git a/src/_backend_agg.cpp b/src/_backend_agg.cpp
index 73e4a1ec9589..fa813eecc184 100644
--- a/src/_backend_agg.cpp
+++ b/src/_backend_agg.cpp
@@ -422,9 +422,8 @@ RendererAgg::create_alpha_buffers()
 {
     if (!alphaBuffer)
     {
-        unsigned stride(width*4);
-        alphaBuffer = new agg::int8u[NUMBYTES];
-        alphaMaskRenderingBuffer.attach(alphaBuffer, width, height, stride);
+        alphaBuffer = new agg::int8u[width * height];
+        alphaMaskRenderingBuffer.attach(alphaBuffer, width, height, width);
         rendererBaseAlphaMask.attach(pixfmtAlphaMask);
         rendererAlphaMask.attach(rendererBaseAlphaMask);
     }
@@ -1120,7 +1119,7 @@ RendererAgg::draw_image(const Py::Tuple& args)
             renderer_type_alpha ri(r, sa, spans);
 
             theRasterizer.add_path(rect2);
-            agg::render_scanlines(theRasterizer, slineP8, ri);
+            agg::render_scanlines(theRasterizer, scanlineAlphaMask, ri);
         }
         else
         {
@@ -1178,7 +1177,7 @@ void RendererAgg::_draw_path(path_t& path, bool has_clippath,
                 amask_ren_type r(pfa);
                 amask_aa_renderer_type ren(r);
                 ren.color(face.second);
-                agg::render_scanlines(theRasterizer, slineP8, ren);
+                agg::render_scanlines(theRasterizer, scanlineAlphaMask, ren);
             }
             else
             {
@@ -1194,7 +1193,7 @@ void RendererAgg::_draw_path(path_t& path, bool has_clippath,
                 amask_ren_type r(pfa);
                 amask_bin_renderer_type ren(r);
                 ren.color(face.second);
-                agg::render_scanlines(theRasterizer, slineP8, ren);
+                agg::render_scanlines(theRasterizer, scanlineAlphaMask, ren);
             }
             else
             {
@@ -1304,7 +1303,7 @@ void RendererAgg::_draw_path(path_t& path, bool has_clippath,
                 amask_ren_type r(pfa);
                 amask_aa_renderer_type ren(r);
                 ren.color(gc.color);
-                agg::render_scanlines(theRasterizer, slineP8, ren);
+                agg::render_scanlines(theRasterizer, scanlineAlphaMask, ren);
             }
             else
             {
@@ -1320,7 +1319,7 @@ void RendererAgg::_draw_path(path_t& path, bool has_clippath,
                 amask_ren_type r(pfa);
                 amask_bin_renderer_type ren(r);
                 ren.color(gc.color);
-                agg::render_scanlines(theRasterizer, slineP8, ren);
+                agg::render_scanlines(theRasterizer, scanlineAlphaMask, ren);
             }
             else
             {
@@ -1902,7 +1901,7 @@ RendererAgg::_draw_gouraud_triangle(const double* points,
         pixfmt_amask_type pfa(pixFmt, alphaMask);
         amask_ren_type r(pfa);
         amask_aa_renderer_type ren(r, span_alloc, span_gen);
-        agg::render_scanlines(theRasterizer, slineP8, ren);
+        agg::render_scanlines(theRasterizer, scanlineAlphaMask, ren);
     }
     else
     {
diff --git a/src/_backend_agg.h b/src/_backend_agg.h
index 7d47ee397031..d1d200ee9ee4 100644
--- a/src/_backend_agg.h
+++ b/src/_backend_agg.h
@@ -62,6 +62,7 @@ typedef agg::rasterizer_scanline_aa<agg::rasterizer_sl_clip_dbl> rasterizer;
 typedef agg::scanline_p8 scanline_p8;
 typedef agg::scanline_bin scanline_bin;
 typedef agg::amask_no_clip_gray8 alpha_mask_type;
+typedef agg::scanline_u8_am<alpha_mask_type> scanline_am;
 
 typedef agg::renderer_base<agg::pixfmt_gray8> renderer_base_alpha_mask_type;
 typedef agg::renderer_scanline_aa_solid<renderer_base_alpha_mask_type> renderer_alpha_mask_type;
@@ -215,7 +216,7 @@ class RendererAgg: public Py::PythonExtension<RendererAgg>
     agg::pixfmt_gray8 pixfmtAlphaMask;
     renderer_base_alpha_mask_type rendererBaseAlphaMask;
     renderer_alpha_mask_type rendererAlphaMask;
-    agg::scanline_p8 scanlineAlphaMask;
+    scanline_am scanlineAlphaMask;
 
     scanline_p8 slineP8;
     scanline_bin slineBin;