diff --git a/pytential/symbolic/mappers.py b/pytential/symbolic/mappers.py
index d77464923cac33910ebeb46a3b336267a017f1d2..cca6b91983eeefa4c7b3e0113db671893917961f 100644
--- a/pytential/symbolic/mappers.py
+++ b/pytential/symbolic/mappers.py
@@ -404,12 +404,12 @@ class QBXPreprocessor(IdentityMapper):
 
         if not is_self:
             # non-self evaluation
-            if expr.qbx_forced_limit == 'avg':
-                from warnings import warn
-                warn("qbx_forced_limit == 'avg' is deprecated "
-                        "for non-self evaluation, defaulting to 'None'",
-                        DeprecationWarning)
-                expr = expr.copy(qbx_forced_limit=None)
+            if expr.qbx_forced_limit in ['avg', 1, -1]:
+                raise ValueError("May not specify +/-1 or \"avg\" for "
+                        "qbx_forced_limit for non-self evaluation. "
+                        "Specify 'None' for automatic choice or +/-2 "
+                        "to force a QBX side in the near-evaluation "
+                        "regime.")
 
             return expr
 
@@ -419,9 +419,9 @@ class QBXPreprocessor(IdentityMapper):
 
         if (isinstance(expr.qbx_forced_limit, int)
                 and abs(expr.qbx_forced_limit) == 2):
-            warn("qbx_forced_limit == +/-2 is deprecated "
-                    "for self evaluation--must require evaluation side",
-                    DeprecationWarning)
+            raise ValueError("May not specify qbx_forced_limit == +/-2 "
+                    "for self-evaluation. "
+                    "Specify +/-1 or \"avg\" instead.")
 
         if expr.qbx_forced_limit == "avg":
             return 0.5*(