diff -r a45cce906207 -r dfd434203aa0 src/jdk.compiler/share/classes/com/sun/tools/javac/file/Locations.java
--- a/src/jdk.compiler/share/classes/com/sun/tools/javac/file/Locations.java	Tue Jul 23 16:52:38 2019 +0200
+++ b/src/jdk.compiler/share/classes/com/sun/tools/javac/file/Locations.java	Wed Sep 18 10:41:18 2019 +0200
@@ -94,6 +94,7 @@
 import com.sun.tools.javac.util.Pair;
 import com.sun.tools.javac.util.StringUtils;
 
+import static javax.tools.StandardLocation.SYSTEM_MODULES;
 import static javax.tools.StandardLocation.PLATFORM_CLASS_PATH;
 
 import static com.sun.tools.javac.main.Option.BOOT_CLASS_PATH;
@@ -185,6 +186,12 @@
         return h.isDefault();
     }
 
+    boolean isDefaultSystemModulesPath() {
+        SystemModulesLocationHandler h
+                = (SystemModulesLocationHandler) getHandler(SYSTEM_MODULES);
+        return !h.isExplicit();
+    }
+
     /**
      * Split a search path into its elements. Empty path elements will be ignored.
      *