1 files changed, 1 insertions, 1 deletions
diff --git a/insns.def b/insns.def
index 3c185bd084..df65aa8efd 100644
--- a/insns.def
+++ b/insns.def
@@ -1262,7 +1262,7 @@ opt_case_dispatch
     switch(TYPE(key)) {
       case T_FLOAT: {
 	double ival;
-	if (modf(RFLOAT_VALUE(key), &ival) == 0.0) {
+	if (modf(RFLOAT_VALUE(key), &ival) == 0.0 && !isinf(ival)) {
 	    key = FIXABLE(ival) ? LONG2FIX((long)ival) : rb_dbl2big(ival);
 	}
       }