diff --git a/sexp.c b/sexp.c
index 9ed817e6..41ece5e4 100644
--- a/sexp.c
+++ b/sexp.c
@@ -2478,7 +2478,7 @@ sexp sexp_read_float_tail (sexp ctx, sexp in, double whole, int negp) {
 #endif
   }
   if (e != 0.0)
-    val = abs(e) > 320 ? exp(log(val) + e*M_LN10) : val * pow(10, e);
+    val = fabsl(e) > 320 ? exp(log(val) + e*M_LN10) : val * pow(10, e);
 #if SEXP_USE_FLONUMS
   res = sexp_make_flonum(ctx, val);
 #else