diff --git a/pyslim/util.py b/pyslim/util.py
index bd304559..01d1edc3 100644
--- a/pyslim/util.py
+++ b/pyslim/util.py
@@ -11,10 +11,13 @@ def unique_labels_by_group(group, label, minlength=0):
     In other words, if the result is ``x``, then
     ``x[j]`` is ``len(set(label[group == j])) == 1``.
     '''
-    n = np.bincount(1 + group, minlength=minlength + 1)[1:]
-    x = np.bincount(1 + group, weights=label, minlength=minlength + 1)[1:]
-    x2 = np.bincount(1 + group, weights=label.astype("int64") ** 2, minlength=minlength + 1)[1:]
-    # (a * x)**2 = a * (a * x**2)
-    return np.logical_and(n > 0, x**2 == n * x2)
-
-
+    w = label.astype("float64")
+    n = np.bincount(1 + group, minlength=minlength + 1)
+    x = np.bincount(1 + group, weights=w, minlength=minlength + 1)
+    with np.errstate(divide='ignore', invalid='ignore'):
+        xm = x/n
+    xm[n == 0] = 0
+    w -= xm[1 + group]
+    gw = np.bincount(1 + group, weights=np.abs(w), minlength=minlength + 1)[1:]
+    # after subtracting groupwise means, should be all zero
+    return np.logical_and(n[1:] > 0, np.abs(gw) < 1e-7)
diff --git a/tests/test_util.py b/tests/test_util.py
index 6445e43b..d73f7f43 100644
--- a/tests/test_util.py
+++ b/tests/test_util.py
@@ -16,9 +16,10 @@ def verify_unique_labels_by_group(self, group, label, minlength):
         x = pyslim.util.unique_labels_by_group(group, label, minlength)
         self.assertGreaterEqual(len(x), minlength)
         for g in range(len(x)):
-            if g != -1:
-                u = set(label[group == g])
-                self.assertEqual(len(u) == 1, x[g])
+            u = set(label[group == g])
+            if (len(u) == 1) != x[g]:
+                print(g, u, x[g], label[group == g], label.dtype)
+            self.assertEqual(len(u) == 1, x[g])
 
     def test_all_same(self):
         n = 10
@@ -50,12 +51,19 @@ def test_all_unique(self):
         self.assertTrue(np.all(x))
 
     def test_unique_labels_by_group(self):
+        np.random.seed(23)
         for ng in 3 * np.arange(2, 15):
             for n in (10, 100):
                 for nl in (2, ng):
                     for minl in (-5, 10000000):
                         group = np.random.choice(np.arange(ng) - 1, size=n)
+                        # "integer" labels
                         label = minl + np.random.choice(np.arange(nl), size=n)
                         self.verify_unique_labels_by_group(group, label, ng)
+                        # int32 labels
+                        self.verify_unique_labels_by_group(group, label.astype("int32"), ng)
+                        # and float labels
+                        label = minl + np.random.choice(np.random.uniform(0, 1, nl), size=n)
+                        self.verify_unique_labels_by_group(group, label, ng)