diff --git a/TODO b/TODO
index d4824cc6..fc007c98 100644
--- a/TODO
+++ b/TODO
@@ -10,6 +10,8 @@ Before Release:
   * Cache environment variables
   * Remove coverage cases for things that are heavily exercised or are
     in critical paths
+* Make ./performance_check usable by other people by having published
+  files to use for testing.
 * Evaluate issues tagged with `next`
 * Stay on top of https://github.com/pikepdf/pikepdf/pull/315
 
diff --git a/libqpdf/QTC.cc b/libqpdf/QTC.cc
index d27bfa8b..21d240ba 100644
--- a/libqpdf/QTC.cc
+++ b/libqpdf/QTC.cc
@@ -2,6 +2,7 @@
 
 #include <qpdf/QUtil.hh>
 #include <set>
+#include <map>
 #include <stdio.h>
 
 static bool
@@ -14,12 +15,19 @@ tc_active(char const* const scope)
 void
 QTC::TC(char const* const scope, char const* const ccase, int n)
 {
-    static std::set<std::pair<std::string, int>> cache;
+    static std::map<std::string, bool> active;
+    auto is_active = active.find(scope);
+    if (is_active == active.end()) {
+        active[scope] = tc_active(scope);
+        is_active = active.find(scope);
+    }
 
-    if (!tc_active(scope)) {
+    if (!is_active->second) {
         return;
     }
 
+    static std::set<std::pair<std::string, int>> cache;
+
     std::string filename;
 #ifdef _WIN32
 # define TC_ENV "TC_WIN_FILENAME"