diff --git a/wecopttool/core.py b/wecopttool/core.py
index b6e7ac1e..ed105b05 100644
--- a/wecopttool/core.py
+++ b/wecopttool/core.py
@@ -2354,10 +2354,14 @@ def subset_close(
 
     ind = []
     for el in set_a:
-        b_in_a = np.isclose(set_b, el,
+        a_in_b = np.isclose(set_b, el,
                             rtol=rtol, atol=atol, equal_nan=equal_nan)
-        if b_in_a.any():
-            ind.append(np.flatnonzero(b_in_a))
+        if np.sum(a_in_b) == 1:
+            ind.append(np.flatnonzero(a_in_b)[0])
+        if np.sum(a_in_b) > 1:
+            _log.warning('Multiple matching elements in subset, ' +
+                         'selecting closest match.')
+            ind.append(np.argmin(np.abs(a_in_b - el)))
     subset = len(set_a) == len(ind)
     ind = ind if subset else []
     return subset, ind