diff --git a/sexp.c b/sexp.c
index c2ce49c4..10e45376 100644
--- a/sexp.c
+++ b/sexp.c
@@ -1913,9 +1913,12 @@ sexp sexp_write_one (sexp ctx, sexp obj, sexp out) {
       } else
 #endif
       {
-        i = snprintf(numbuf, NUMBUF_LEN, "%.16lg", f);
-        if (i >= 16 && sscanf(numbuf, "%lg", &ftmp) == 1 && ftmp != f) {
-          i = snprintf(numbuf, NUMBUF_LEN, "%.17lg", f);
+        i = snprintf(numbuf, NUMBUF_LEN, "%.15lg", f);
+        if (i >= 15 && sscanf(numbuf, "%lg", &ftmp) == 1 && ftmp != f) {
+          i = snprintf(numbuf, NUMBUF_LEN, "%.16lg", f);
+          if (i >= 16 && sscanf(numbuf, "%lg", &ftmp) == 1 && ftmp != f) {
+            i = snprintf(numbuf, NUMBUF_LEN, "%.17lg", f);
+          }
         }
         if (!strchr(numbuf, '.') && !strchr(numbuf, 'e')) {
           numbuf[i++] = '.'; numbuf[i++] = '0'; numbuf[i++] = '\0';
diff --git a/tests/r7rs-tests.scm b/tests/r7rs-tests.scm
index 3caf551b..1ec27a38 100644
--- a/tests/r7rs-tests.scm
+++ b/tests/r7rs-tests.scm
@@ -2366,13 +2366,13 @@
            (eqv? n (string->number (car ls)))))))))
 
 (test-precision "-1.7976931348623157e+308" "-inf.0")
-(test-precision "4.940656458412465e-324" "5.0e-324" "0.0")
-(test-precision "9.881312916824931e-324" "1.0e-323" "0.0")
+(test-precision "4.940656458412465e-324" "4.94065645841247e-324" "5.0e-324" "0.0")
+(test-precision "9.881312916824931e-324" "9.88131291682493e-324" "1.0e-323" "0.0")
 (test-precision "1.48219693752374e-323" "1.5e-323" "0.0")
-(test-precision "1.976262583364986e-323" "2.0e-323" "0.0")
-(test-precision "2.470328229206233e-323" "2.5e-323" "0.0")
-(test-precision "2.420921664622108e-322" "2.4e-322" "0.0")
-(test-precision "2.420921664622108e-320" "2.421e-320" "0.0")
+(test-precision "1.976262583364986e-323" "1.97626258336499e-323" "2.0e-323" "0.0")
+(test-precision "2.470328229206233e-323" "2.47032822920623e-323" "2.5e-323" "0.0")
+(test-precision "2.420921664622108e-322" "2.42092166462211e-322" "2.4e-322" "0.0")
+(test-precision "2.420921664622108e-320" "2.42092166462211e-320" "2.421e-320" "0.0")
 (test-precision "1.4489974452386991" "1.4489975")
 (test-precision "0.14285714285714282" "0.14285714285714288" "0.14285715")
 (test-precision "1.7976931348623157e+308" "+inf.0")