diff --git a/p2-maven-plugin/src/main/java/org/eclipse/tycho/p2maven/transport/RemoteArtifactRepositoryManagerAgentFactory.java b/p2-maven-plugin/src/main/java/org/eclipse/tycho/p2maven/transport/RemoteArtifactRepositoryManagerAgentFactory.java
index 0fbf24d22e..f41fc4e2dc 100644
--- a/p2-maven-plugin/src/main/java/org/eclipse/tycho/p2maven/transport/RemoteArtifactRepositoryManagerAgentFactory.java
+++ b/p2-maven-plugin/src/main/java/org/eclipse/tycho/p2maven/transport/RemoteArtifactRepositoryManagerAgentFactory.java
@@ -72,11 +72,11 @@ private boolean getDisableP2MirrorsConfiguration() {
 
 	private String getMirrorProperty(String key) {
 		String value = System.getProperty(key);
-		if (key == null && mavenContext.getSession() != null) {
-			key = mavenContext.getSession().getSystemProperties().getProperty(key);
+		if (value == null && mavenContext.getSession() != null) {
+			value = mavenContext.getSession().getSystemProperties().getProperty(key);
 
-			if (key == null) {
-				key = mavenContext.getSession().getUserProperties().getProperty(key);
+			if (value == null) {
+				value = mavenContext.getSession().getUserProperties().getProperty(key);
 			}
 		}
 		return value;