diff --git a/oak-core/src/main/java/org/apache/jackrabbit/oak/namepath/impl/LocalNameMapper.java b/oak-core/src/main/java/org/apache/jackrabbit/oak/namepath/impl/LocalNameMapper.java
index fe688f92519..a1d5d40471a 100644
--- a/oak-core/src/main/java/org/apache/jackrabbit/oak/namepath/impl/LocalNameMapper.java
+++ b/oak-core/src/main/java/org/apache/jackrabbit/oak/namepath/impl/LocalNameMapper.java
@@ -58,16 +58,13 @@ public synchronized String getJcrName(@NotNull String oakName) {
         checkArgument(!oakName.startsWith(":"), oakName); // hidden name
         checkArgument(!isExpandedName(oakName), oakName); // expanded name
 
-        if (!local.isEmpty()) {
-            int colon = oakName.indexOf(':');
-            if (colon > 0) {
-                String oakPrefix = oakName.substring(0, colon);
-                String uri = getNamespacesProperty(oakPrefix);
-                if (uri == null) {
-                    throw new IllegalStateException(
-                            "No namespace mapping found for " + oakName);
-                }
+        int colon = oakName.indexOf(':');
+        if (colon > 0) {
+            String oakPrefix = oakName.substring(0, colon);
+            String uri = getNamespacesProperty(oakPrefix);
 
+            if (local.containsValue(uri)) {
+                //local prefix replaces global prefix
                 for (Map.Entry<String, String> entry : local.entrySet()) {
                     if (uri.equals(entry.getValue())) {
                         String jcrPrefix = entry.getKey();
@@ -78,22 +75,15 @@ public synchronized String getJcrName(@NotNull String oakName) {
                         }
                     }
                 }
-
-                // local mapping not found for this URI, make sure there
-                // is no conflicting local mapping for the prefix
-                if (local.containsKey(oakPrefix)) {
-                    for (int i = 2; true; i++) {
-                        String jcrPrefix = oakPrefix + i;
-                        if (!local.containsKey(jcrPrefix)) {
-                            log.warn("no prefix found for namespace name '" + uri + "', using unmapped temporary prefix '"
-                                    + jcrPrefix + "' for now (see OAK-10544)");
-                            return jcrPrefix + oakName.substring(colon);
-                        }
-                    }
-                }
+            } else if (uri == null && !local.containsKey(oakPrefix)) {
+                //completely unknown prefix
+                throw new IllegalStateException("No namespace mapping found for " + oakName);
             }
         }
 
+        //locally registered, but not yet globally known
+        //or globally known, but not locally overridden
+        //or empty namespace
         return oakName;
     }
 
diff --git a/oak-jcr/src/test/java/org/apache/jackrabbit/oak/jcr/JackrabbitNodeTest.java b/oak-jcr/src/test/java/org/apache/jackrabbit/oak/jcr/JackrabbitNodeTest.java
index 223102839ae..0c4212e9c11 100644
--- a/oak-jcr/src/test/java/org/apache/jackrabbit/oak/jcr/JackrabbitNodeTest.java
+++ b/oak-jcr/src/test/java/org/apache/jackrabbit/oak/jcr/JackrabbitNodeTest.java
@@ -24,14 +24,19 @@
 import java.util.List;
 import java.util.concurrent.CountDownLatch;
 
+import javax.jcr.ItemExistsException;
 import javax.jcr.Node;
 import javax.jcr.NodeIterator;
+import javax.jcr.PathNotFoundException;
 import javax.jcr.RepositoryException;
 import javax.jcr.Session;
+import javax.jcr.lock.LockException;
+import javax.jcr.nodetype.ConstraintViolationException;
 import javax.jcr.observation.Event;
 import javax.jcr.observation.EventIterator;
 import javax.jcr.observation.EventListener;
 import javax.jcr.observation.ObservationManager;
+import javax.jcr.version.VersionException;
 
 import org.apache.jackrabbit.JcrConstants;
 import org.apache.jackrabbit.api.JackrabbitNode;
@@ -336,4 +341,11 @@ public void testGetPropertyOrNull() throws Exception {
         assertNotNull(jn.getPropertyOrNull(JcrConstants.JCR_PRIMARYTYPE));
         assertNotNull(jn.getPropertyOrNull("a/aa/p"));
     }
+    
+    public void testSessionMappedPrefixWithUnregisteredNamespace() throws ItemExistsException, PathNotFoundException, VersionException, ConstraintViolationException, LockException, RepositoryException {
+        Node n = testRootNode.addNode("foo:bar");
+        assertEquals("foo:bar", n.getName());
+        n.getSession().setNamespacePrefix("foo", "http://foo.com");
+        assertEquals("foo:bar", n.getName()); // this must not fail, but throws a ISE
+    }
 }