diff --git a/LOG b/LOG
index 9b161f4afb..36b1851034 100644
--- a/LOG
+++ b/LOG
@@ -36,3 +36,6 @@
   zlib and nanopass, since they are logically part of the git clone.
   It does run make distclean in zlib.
     makefiles/Makefile.in
+- converted s_test_schlib shifts of -1 to equivalent shifts of 1 to
+  avoid undefined left-shift behavior on negative numbers.
+    prim5.c
diff --git a/c/prim5.c b/c/prim5.c
index c4d1031656..6793a18b7f 100644
--- a/c/prim5.c
+++ b/c/prim5.c
@@ -1686,8 +1686,8 @@ static void s_test_schlib() {
   INT test = 0;
   I32 n1 = 0x73215609;
   I64 n2 = n1 * 37;
-  I32 n3 = (I32)-1<<31;
-  I64 n4 = (I64)-1<<63;
+  I32 n3 = (I32)1<<31;
+  I64 n4 = (I64)1<<63;
   I32 n5 = -1;
 
   SCHLIBTEST(Sinteger_value(Sinteger(n1)) == n1)