diff --git a/genrule/genrule.go b/genrule/genrule.go
index 8282426..2ddd70e 100644
--- a/genrule/genrule.go
+++ b/genrule/genrule.go
@@ -496,7 +496,7 @@
 						}
 						return paths[0], nil
 					} else {
-						return reportError("unknown location label %q", label)
+						return reportError("unknown location label %q is not in srcs, out, tools or tool_files.", label)
 					}
 				} else if strings.HasPrefix(name, "locations ") {
 					label := strings.TrimSpace(strings.TrimPrefix(name, "locations "))
@@ -507,7 +507,7 @@
 						}
 						return strings.Join(paths, " "), nil
 					} else {
-						return reportError("unknown locations label %q", label)
+						return reportError("unknown locations label %q is not in srcs, out, tools or tool_files.", label)
 					}
 				} else {
 					return reportError("unknown variable '$(%s)'", name)
diff --git a/genrule/genrule_test.go b/genrule/genrule_test.go
index 04c97fd..1b5cef2 100644
--- a/genrule/genrule_test.go
+++ b/genrule/genrule_test.go
@@ -341,7 +341,7 @@
 				out: ["out"],
 				cmd: "echo foo > $(location missing)",
 			`,
-			err: `unknown location label "missing"`,
+			err: `unknown location label "missing" is not in srcs, out, tools or tool_files.`,
 		},
 		{
 			name: "error locations",
@@ -349,7 +349,7 @@
 					out: ["out"],
 					cmd: "echo foo > $(locations missing)",
 			`,
-			err: `unknown locations label "missing"`,
+			err: `unknown locations label "missing" is not in srcs, out, tools or tool_files`,
 		},
 		{
 			name: "error location no files",