diff --git a/tycho-core/src/main/java/org/eclipse/tycho/p2resolver/TargetPlatformFactoryImpl.java b/tycho-core/src/main/java/org/eclipse/tycho/p2resolver/TargetPlatformFactoryImpl.java
index 82c410df41..ff5f396bf8 100644
--- a/tycho-core/src/main/java/org/eclipse/tycho/p2resolver/TargetPlatformFactoryImpl.java
+++ b/tycho-core/src/main/java/org/eclipse/tycho/p2resolver/TargetPlatformFactoryImpl.java
@@ -264,8 +264,10 @@ public P2TargetPlatform createTargetPlatform(TargetPlatformConfigurationStub tpC
                 return Optional.empty();
             }).ifPresent(externalUIs::add);
         }
-        //add p2.inf items...
-        gatherP2InfUnits(project, externalUIs);
+        //add p2.inf extra units from all projects...
+        for (ReactorProject reactorProject : reactorProjects) {
+            gatherP2InfUnits(reactorProject, externalUIs);
+        }
 
         Map<IInstallableUnit, ReactorProjectIdentities> reactorProjectUIs = getPreliminaryReactorProjectUIs(
                 reactorProjects);