diff -r c7908e8c786b -r 8b6a878d8773 langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Modules.java
--- a/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Modules.java	Thu Sep 01 10:30:50 2016 +0200
+++ b/langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Modules.java	Mon Aug 29 15:53:03 2016 +0200
@@ -392,6 +392,7 @@
                             if (moduleOverride != null) {
                                 checkNoAllModulePath();
                                 defaultModule = moduleFinder.findModule(names.fromString(moduleOverride));
+                                defaultModule.sourceLocation = StandardLocation.SOURCE_PATH;
                             } else {
                                 // Question: why not do findAllModules and initVisiblePackages here?
                                 // i.e. body of unnamedModuleCompleter
@@ -432,7 +433,9 @@
 
             if (defaultModule != syms.unnamedModule) {
                 syms.unnamedModule.completer = getUnnamedModuleCompleter();
-                syms.unnamedModule.sourceLocation = StandardLocation.SOURCE_PATH;
+                if (moduleOverride == null) {
+                    syms.unnamedModule.sourceLocation = StandardLocation.SOURCE_PATH;
+                }
                 syms.unnamedModule.classLocation = StandardLocation.CLASS_PATH;
             }