diff --git a/modules/util/abi_surfrad.py b/modules/util/abi_surfrad.py
index 1e371886f2ed9608a191a0a00ee01088bf5c9423..b3ebbf4c12f8babacfb0c5404fb847c3c79c97e2 100644
--- a/modules/util/abi_surfrad.py
+++ b/modules/util/abi_surfrad.py
@@ -71,14 +71,13 @@ def process_cld_prob(grd_k):
 
 def process_cloud_frac(grd_k):
     keep = np.invert(np.isnan(grd_k))
-    num_keep = np.sum(keep)
 
     grd_by_cat = get_cloud_frac_5cat(grd_k)
-    # if at least 20% mixed pass
-    keep_mix = np.where(keep, np.logical_and(grd_by_cat > 0, grd_by_cat < 4), False)
-    frac_mix = np.sum(keep_mix)/num_keep
-    if frac_mix < 0.20:
+    keep_mix = np.logical_and(grd_by_cat > 0, grd_by_cat < 4)
+    frac_mix = np.sum(keep_mix)/keep_mix.size
+    if frac_mix < 0.20:  # at least 20% mixed to pass
         return None
+
     grd_k = np.where(np.invert(keep), 0, grd_k)  # Convert NaN to 0
     return grd_k