diff --git a/logback-core/src/main/java/ch/qos/logback/core/ContextBase.java b/logback-core/src/main/java/ch/qos/logback/core/ContextBase.java
index 8bd4c148f9..ff8ce6f736 100755
--- a/logback-core/src/main/java/ch/qos/logback/core/ContextBase.java
+++ b/logback-core/src/main/java/ch/qos/logback/core/ContextBase.java
@@ -104,8 +104,8 @@ public void putProperty(String key, String val) {
     }
 
     protected void initCollisionMaps() {
-        putObject(FA_FILENAME_COLLISION_MAP, new HashMap<String, String>());
-        putObject(RFA_FILENAME_PATTERN_COLLISION_MAP, new HashMap<String, FileNamePattern>());
+        putObject(FA_FILENAME_COLLISION_MAP, new ConcurrentHashMap<String, String>());
+        putObject(RFA_FILENAME_PATTERN_COLLISION_MAP, new ConcurrentHashMap<String, FileNamePattern>());
     }
 
     @Override