diff --git a/src/groupmesh.cpp b/src/groupmesh.cpp
index dfeb0104..da04ce1c 100644
--- a/src/groupmesh.cpp
+++ b/src/groupmesh.cpp
@@ -637,6 +637,7 @@ void Group::DrawFilledPaths(Canvas *canvas) {
         SPolygon sp = {};
         sbls.MakePwlInto(&sp);
         canvas->DrawPolygon(sp, hcf);
+        sp.Clear();
     }
 }
 
diff --git a/src/render/render.cpp b/src/render/render.cpp
index 62f01b35..a1e14dd4 100644
--- a/src/render/render.cpp
+++ b/src/render/render.cpp
@@ -144,6 +144,11 @@ bool Canvas::Fill::Equals(const Fill &other) const {
             pattern == other.pattern);
 }
 
+void Canvas::Clear() {
+    strokes.Clear();
+    fills.Clear();
+}
+
 Canvas::hStroke Canvas::GetStroke(const Stroke &stroke) {
     for(const Stroke &s : strokes) {
         if(s.Equals(stroke)) return s.h;
diff --git a/src/render/render.h b/src/render/render.h
index f74b522b..87fb0218 100644
--- a/src/render/render.h
+++ b/src/render/render.h
@@ -98,6 +98,7 @@ public:
         StipplePattern  stipplePattern;
         double          stippleScale;
 
+        void Clear() { *this = {}; }
         bool Equals(const Stroke &other) const;
     };
 
@@ -114,13 +115,15 @@ public:
         RgbaColor       color;
         FillPattern     pattern;
 
+        void Clear() { *this = {}; }
         bool Equals(const Fill &other) const;
     };
 
     IdList<Stroke, hStroke> strokes;
     IdList<Fill,   hFill>   fills;
 
-    Canvas() : strokes(), fills() {};
+    Canvas() : strokes(), fills() {}
+    virtual void Clear();
 
     hStroke GetStroke(const Stroke &stroke);
     hFill GetFill(const Fill &fill);
@@ -226,7 +229,7 @@ public:
     BBox        bbox;
 
     SurfaceRenderer() : camera(), lighting(), chordTolerance(), mesh(), bbox() {}
-    virtual void Clear();
+    void Clear() override;
 
     // Canvas interface.
     const Camera &GetCamera() const override { return camera; }
diff --git a/src/render/render2d.cpp b/src/render/render2d.cpp
index 53c29522..6ce1c009 100644
--- a/src/render/render2d.cpp
+++ b/src/render/render2d.cpp
@@ -352,6 +352,8 @@ void SurfaceRenderer::OutputInPaintOrder() {
                 if(tr.meta.color.IsEmpty()) continue;
                 OutputTriangle(tr);
             }
+
+            mp.Clear();
         }
 
         for(auto eit : edges) {
@@ -382,6 +384,8 @@ void SurfaceRenderer::OutputInPaintOrder() {
 }
 
 void SurfaceRenderer::Clear() {
+    Canvas::Clear();
+
     for(auto &eit : edges) {
         SEdgeList &el = eit.second;
         el.l.Clear();
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 096f1192..c0ed0d20 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -2,7 +2,8 @@
 
 include_directories(
     ${CMAKE_CURRENT_SOURCE_DIR}
-    ${CMAKE_CURRENT_BINARY_DIR})
+    ${CMAKE_CURRENT_BINARY_DIR}
+    ${CAIRO_INCLUDE_DIRS})
 
 set(testsuite_SOURCES
     harness.cpp
diff --git a/test/harness.cpp b/test/harness.cpp
index 4547cd8a..b819596a 100644
--- a/test/harness.cpp
+++ b/test/harness.cpp
@@ -5,6 +5,7 @@
 //-----------------------------------------------------------------------------
 #include "harness.h"
 #include <regex>
+#include <cairo.h>
 #if defined(WIN32)
 #include <windows.h>
 #else
@@ -310,11 +311,15 @@ int main(int argc, char **argv) {
     if(failTally > 0) {
         fprintf(stderr, "Failure! %u checks failed\n",
                 (unsigned)failTally);
-        return 1;
     } else {
         fprintf(stderr, "Success! %u test cases (%u skipped), %u checks, %.3fs\n",
                 (unsigned)ranTally, (unsigned)skippedTally,
                 (unsigned)checkTally, testTime.count());
-        return 0;
     }
+
+    // At last, try to reset all caches we or our dependencies have, to make SNR
+    // of memory checking tools like valgrind higher.
+    cairo_debug_reset_static_data();
+
+    return (failTally > 0);
 }