diff --git a/app/src/processing/app/contrib/ContributionListing.java b/app/src/processing/app/contrib/ContributionListing.java
index 1e0915c78..2cd572e94 100644
--- a/app/src/processing/app/contrib/ContributionListing.java
+++ b/app/src/processing/app/contrib/ContributionListing.java
@@ -123,7 +123,9 @@ public class ContributionListing {
 
       if (oldLib.getImports() != null) {
         for (String importName : oldLib.getImports()) {
-          librariesByImportHeader.replace(importName, newLib);
+          if (librariesByImportHeader.containsKey(importName)) {
+            librariesByImportHeader.put(importName, newLib);
+          }
         }
       }