diff --git a/src/org/labkey/test/params/FieldKey.java b/src/org/labkey/test/params/FieldKey.java
index 1469033737..eb3100a331 100644
--- a/src/org/labkey/test/params/FieldKey.java
+++ b/src/org/labkey/test/params/FieldKey.java
@@ -2,6 +2,7 @@
 
 import org.apache.commons.lang3.StringUtils;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -65,7 +66,7 @@ public static FieldKey fromParts(String... parts)
      * @param fieldKey String or FieldKey
      * @return FieldKey representation of the String, or the identity if a FieldKey was provided
      */
-    public static FieldKey fromFieldKey(CharSequence fieldKey)
+    public static @Nullable FieldKey fromFieldKey(CharSequence fieldKey)
     {
         if (fieldKey instanceof WrapsFieldKey fk)
         {
@@ -73,7 +74,14 @@ public static FieldKey fromFieldKey(CharSequence fieldKey)
         }
         else
         {
-            return fromParts(Arrays.stream(fieldKey.toString().split(SEPARATOR)).map(FieldKey::decodePart).toList());
+            try
+            {
+                return fromParts(Arrays.stream(fieldKey.toString().split(SEPARATOR)).map(FieldKey::decodePart).toList());
+            }
+            catch (IllegalArgumentException iae)
+            {
+                return null; // FieldReferenceManager depends on this returning null.
+            }
         }
     }