diff --git a/api/src/org/labkey/filters/ContentSecurityPolicyFilter.java b/api/src/org/labkey/filters/ContentSecurityPolicyFilter.java
index 64e645b7c76..c2eacd89ba3 100644
--- a/api/src/org/labkey/filters/ContentSecurityPolicyFilter.java
+++ b/api/src/org/labkey/filters/ContentSecurityPolicyFilter.java
@@ -372,6 +372,8 @@ public void testSubstitutionMap()
         {
             synchronized (ALLOWED_SOURCES_LOCK)
             {
+                // Ensure substitution map has been initialized, otherwise the finally block asserts will fail
+                regenerateSubstitutionMap();
                 // Make a deep copy of ALLOWED_SOURCES so we can restore it after testing
                 int sourceMapSize = ALLOWED_SOURCES.size();
                 int substitutionMapSize = ALLOWED_SOURCES_SUBSTITUTION_MAP.size();