diff --git a/src/main/java/gov/usgs/earthquake/nshmp/www/services/MaxDirection.java b/src/main/java/gov/usgs/earthquake/nshmp/www/services/MaxDirection.java
index 9f377c661a6e11135d1a7cec63c6be7c805691bd..e35c59355037416482937ce865aeee59400af2cf 100644
--- a/src/main/java/gov/usgs/earthquake/nshmp/www/services/MaxDirection.java
+++ b/src/main/java/gov/usgs/earthquake/nshmp/www/services/MaxDirection.java
@@ -23,41 +23,43 @@ import static gov.usgs.earthquake.nshmp.gmm.Imt.SA4P0;
 import static gov.usgs.earthquake.nshmp.gmm.Imt.SA5P0;
 import static gov.usgs.earthquake.nshmp.gmm.Imt.SA7P5;
 
+import java.util.Collections;
 import java.util.EnumMap;
 import java.util.Map;
 
 import gov.usgs.earthquake.nshmp.gmm.Imt;
 
 /*
- * Max direction factors derived from Shahi and Baker (2012) and used in the
- * BSSC.
+ * Max direction map derived from Shahi and Baker (2012) and used in the BSSC.
  */
 class MaxDirection {
 
-  static final Map<Imt, Double> FACTORS = new EnumMap<>(Imt.class);
+  static final Map<Imt, Double> FACTORS;
 
   static {
-    FACTORS.put(PGA, 1.0);
-    FACTORS.put(SA0P01, 1.200);
-    FACTORS.put(SA0P02, 1.200);
-    FACTORS.put(SA0P03, 1.200);
-    FACTORS.put(SA0P05, 1.200);
-    FACTORS.put(SA0P075, 1.200);
-    FACTORS.put(SA0P1, 1.200);
-    FACTORS.put(SA0P15, 1.200);
-    FACTORS.put(SA0P2, 1.200);
-    FACTORS.put(SA0P25, 1.203);
-    FACTORS.put(SA0P3, 1.206);
-    FACTORS.put(SA0P4, 1.213);
-    FACTORS.put(SA0P5, 1.219);
-    FACTORS.put(SA0P75, 1.234);
-    FACTORS.put(SA1P0, 1.250);
-    FACTORS.put(SA1P5, 1.253);
-    FACTORS.put(SA2P0, 1.256);
-    FACTORS.put(SA3P0, 1.261);
-    FACTORS.put(SA4P0, 1.267);
-    FACTORS.put(SA5P0, 1.272);
-    FACTORS.put(SA7P5, 1.286);
-    FACTORS.put(SA10P0, 1.300);
+    Map<Imt, Double> map = new EnumMap<>(Imt.class);
+    map.put(PGA, 1.0);
+    map.put(SA0P01, 1.200);
+    map.put(SA0P02, 1.200);
+    map.put(SA0P03, 1.200);
+    map.put(SA0P05, 1.200);
+    map.put(SA0P075, 1.200);
+    map.put(SA0P1, 1.200);
+    map.put(SA0P15, 1.200);
+    map.put(SA0P2, 1.200);
+    map.put(SA0P25, 1.203);
+    map.put(SA0P3, 1.206);
+    map.put(SA0P4, 1.213);
+    map.put(SA0P5, 1.219);
+    map.put(SA0P75, 1.234);
+    map.put(SA1P0, 1.250);
+    map.put(SA1P5, 1.253);
+    map.put(SA2P0, 1.256);
+    map.put(SA3P0, 1.261);
+    map.put(SA4P0, 1.267);
+    map.put(SA5P0, 1.272);
+    map.put(SA7P5, 1.286);
+    map.put(SA10P0, 1.300);
+    FACTORS = Collections.unmodifiableMap(map);
   }
 }