Index: src/ResolvExpr/ResolveAssertions.cc
===================================================================
--- src/ResolvExpr/ResolveAssertions.cc	(revision 21300d75a007db91aebde37600bdcb7eeb14a5d5)
+++ src/ResolvExpr/ResolveAssertions.cc	(revision 462a7c71b73f09a9b66be205a97e657e38d1196c)
@@ -325,5 +325,6 @@
 					entry.second.expr = postmutate( entry.second.expr );
 					// xxx - look at entry.second.inferParams?
-					expr->inferParams[ entry.first ] = entry.second;
+					auto res = expr->inferParams.emplace( entry.first, entry.second );
+					assert(res.second);
 				}
 			}