diff --git a/fstest/test_all/run.go b/fstest/test_all/run.go
index 2c45c73d2..f156b7f18 100644
--- a/fstest/test_all/run.go
+++ b/fstest/test_all/run.go
@@ -100,33 +100,53 @@ func (r *Run) dumpOutput() {
 	log.Println("------------------------------------------------------------")
 }
 
+// trie for storing runs
+type trie map[string]trie
+
+// turn a trie into multiple regexp matches
+//
+// We can't ever have a / in a regexp as it doesn't work.
+func match(current trie) []string {
+	var names []string
+	var parts []string
+	for name, value := range current {
+		matchName := "^" + name + "$"
+		if len(value) == 0 {
+			names = append(names, name)
+		} else {
+			for _, part := range match(value) {
+				parts = append(parts, matchName+"/"+part)
+			}
+		}
+	}
+	sort.Strings(names)
+	if len(names) > 1 {
+		parts = append(parts, "^("+strings.Join(names, "|")+")$")
+	} else if len(names) == 1 {
+		parts = append(parts, "^"+names[0]+"$")
+	}
+	sort.Strings(parts)
+	return parts
+}
+
 // This converts a slice of test names into a regexp which matches
 // them.
 func testsToRegexp(tests []string) string {
-	var split []map[string]struct{}
-	// Make a slice with maps of the used parts at each level
+	var split = trie{}
+	// Make a trie showing which parts are used at each level
 	for _, test := range tests {
-		for i, name := range strings.Split(test, "/") {
-			if i >= len(split) {
-				split = append(split, make(map[string]struct{}))
+		var parent = split
+		for _, name := range strings.Split(test, "/") {
+			current := parent[name]
+			if current == nil {
+				current = trie{}
+				parent[name] = current
 			}
-			split[i][name] = struct{}{}
+			parent = current
 		}
 	}
-	var out []string
-	for _, level := range split {
-		var testsInLevel = []string{}
-		for name := range level {
-			testsInLevel = append(testsInLevel, name)
-		}
-		sort.Strings(testsInLevel)
-		if len(testsInLevel) > 1 {
-			out = append(out, "^("+strings.Join(testsInLevel, "|")+")$")
-		} else {
-			out = append(out, "^"+testsInLevel[0]+"$")
-		}
-	}
-	return strings.Join(out, "/")
+	parts := match(split)
+	return strings.Join(parts, "|")
 }
 
 var failRe = regexp.MustCompile(`(?m)^\s*--- FAIL: (Test.*?) \(`)
diff --git a/fstest/test_all/run_test.go b/fstest/test_all/run_test.go
index b51ea3313..060074a6f 100644
--- a/fstest/test_all/run_test.go
+++ b/fstest/test_all/run_test.go
@@ -40,7 +40,7 @@ func TestTestsToRegexp(t *testing.T) {
 				"TestOne/Sub1",
 				"TestTwo",
 			},
-			want: "^(TestOne|TestTwo)$/^Sub1$",
+			want: "^TestOne$/^Sub1$|^TestTwo$",
 		},
 		{
 			in: []string{
@@ -48,7 +48,7 @@ func TestTestsToRegexp(t *testing.T) {
 				"TestOne/Sub2",
 				"TestTwo",
 			},
-			want: "^(TestOne|TestTwo)$/^(Sub1|Sub2)$",
+			want: "^TestOne$/^(Sub1|Sub2)$|^TestTwo$",
 		},
 		{
 			in: []string{
@@ -56,7 +56,7 @@ func TestTestsToRegexp(t *testing.T) {
 				"TestOne/Sub2/SubSub1",
 				"TestTwo",
 			},
-			want: "^(TestOne|TestTwo)$/^(Sub1|Sub2)$/^SubSub1$",
+			want: "^TestOne$/^Sub1$|^TestOne$/^Sub2$/^SubSub1$|^TestTwo$",
 		},
 		{
 			in: []string{
@@ -64,7 +64,7 @@ func TestTestsToRegexp(t *testing.T) {
 				"TestTests/B/B1",
 				"TestTests/C/C3/C31",
 			},
-			want: "^TestTests$/^(A1|B|C)$/^(B1|C3)$/^C31$",
+			want: "^TestTests$/^A1$|^TestTests$/^B$/^B1$|^TestTests$/^C$/^C3$/^C31$",
 		},
 	} {
 		got := testsToRegexp(test.in)
@@ -108,13 +108,11 @@ func TestTestsToRegexpLive(t *testing.T) {
 				"TestTests/B",
 				"TestTests/B/B1",
 				"TestTests/C",
-				// FIXME there doesn't seem to be a way to select a non-terminal test
-				// and all of its subtests if there is a longer path (in this case B/B1)
-				// "TestTests/C/C1",
-				// "TestTests/C/C2",
-				// "TestTests/C/C3",
-				// "TestTests/C/C3/C31",
-				// "TestTests/C/C3/C32",
+				"TestTests/C/C1",
+				"TestTests/C/C2",
+				"TestTests/C/C3",
+				"TestTests/C/C3/C31",
+				"TestTests/C/C3/C32",
 			},
 		},
 		{