diff --git a/lib/Support/APFloat.cpp b/lib/Support/APFloat.cpp
index 8ecfa35..35de714 100644
--- a/lib/Support/APFloat.cpp
+++ b/lib/Support/APFloat.cpp
@@ -1678,6 +1678,7 @@
   opStatus fs;
 
   assertArithmeticOK(*semantics);
+  assertArithmeticOK(toSemantics);
   lostFraction = lfExactlyZero;
   newPartCount = partCountForBits(toSemantics.precision + 1);
   oldPartCount = partCount();