diff --git a/mats/5_3.ms b/mats/5_3.ms
index b9aba3651..416465a1a 100644
--- a/mats/5_3.ms
+++ b/mats/5_3.ms
@@ -2592,6 +2592,14 @@
     (eqv? (lcm 10.0 0.0 0.0 0.0) 0.0)
     (eqv? (lcm 0.0 6.0 7.0 10.0) 0.0)
     (eqv? (lcm 10.0 6.0 7.0 0.0) 0.0)
+    (eqv? (lcm 3E307 5E307) +inf.0)
+    (eqv? (lcm #e3E999 1.0) +inf.0)
+    (begin
+      ;; make sure the optimizer doesn't assume an integer result
+      (define ($lcm-result x) (if (integer? (lcm x 1.0)) 'int 'non-int))
+      #t)
+    (eq? ($lcm-result 5) 'int)
+    (eq? ($lcm-result #e3E999) 'non-int)
  )
 
 (mat expt
diff --git a/s/primdata.ss b/s/primdata.ss
index 8fd3f243b..7650b0a5d 100644
--- a/s/primdata.ss
+++ b/s/primdata.ss
@@ -223,7 +223,7 @@
   (div0 [sig [(real real) -> (real)]] [flags arith-op mifoldable discard])
   (mod0 [sig [(real real) -> (real)]] [flags arith-op mifoldable discard])
   (gcd [sig [(integer ...) -> (integer)]] [flags arith-op mifoldable discard ieee r5rs])
-  (lcm [sig [(integer ...) -> (integer)]] [flags arith-op mifoldable discard ieee r5rs])
+  (lcm [sig [(integer ...) -> (real)]] [flags arith-op mifoldable discard ieee r5rs]) ; uinteger or +inf.0
   (numerator [sig [(rational) -> (integer)]] [flags arith-op mifoldable discard ieee r5rs])
   (denominator [sig [(rational) -> (integer)]] [flags arith-op mifoldable discard ieee r5rs])
   (floor [sig [(real) -> (real)]] [flags arith-op mifoldable discard safeongoodargs ieee r5rs])