diff --git a/test/ruby/test_process.rb b/test/ruby/test_process.rb
index 816751ec81..6f16ac3062 100644
--- a/test/ruby/test_process.rb
+++ b/test/ruby/test_process.rb
@@ -1509,6 +1509,9 @@ class TestProcess < Test::Unit::TestCase
 
   def test_sleep
     assert_raise(ArgumentError) { sleep(1, 1) }
+    [-1, -1.0, -1r].each do |sec|
+      assert_raise_with_message(ArgumentError, /not.*negative/) { sleep(sec) }
+    end
   end
 
   def test_getpgid
diff --git a/time.c b/time.c
index 8d272d91f3..e70899aabc 100644
--- a/time.c
+++ b/time.c
@@ -2524,12 +2524,12 @@ time_timespec(VALUE num, int interval)
     if (FIXNUM_P(num)) {
 	t.tv_sec = NUM2TIMET(num);
 	if (interval && t.tv_sec < 0)
-	    rb_raise(rb_eArgError, "%s must be positive", tstr);
+            rb_raise(rb_eArgError, "%s must not be negative", tstr);
 	t.tv_nsec = 0;
     }
     else if (RB_FLOAT_TYPE_P(num)) {
 	if (interval && RFLOAT_VALUE(num) < 0.0)
-	    rb_raise(rb_eArgError, "%s must be positive", tstr);
+            rb_raise(rb_eArgError, "%s must not be negative", tstr);
 	else {
 	    double f, d;
 
@@ -2554,7 +2554,7 @@ time_timespec(VALUE num, int interval)
     else if (RB_TYPE_P(num, T_BIGNUM)) {
 	t.tv_sec = NUM2TIMET(num);
 	if (interval && t.tv_sec < 0)
-	    rb_raise(rb_eArgError, "%s must be positive", tstr);
+            rb_raise(rb_eArgError, "%s must not be negative", tstr);
 	t.tv_nsec = 0;
     }
     else {
@@ -2565,7 +2565,7 @@ time_timespec(VALUE num, int interval)
             f = rb_ary_entry(ary, 1);
             t.tv_sec = NUM2TIMET(i);
             if (interval && t.tv_sec < 0)
-                rb_raise(rb_eArgError, "%s must be positive", tstr);
+                rb_raise(rb_eArgError, "%s must not be negative", tstr);
             f = rb_funcall(f, '*', 1, INT2FIX(1000000000));
             t.tv_nsec = NUM2LONG(f);
         }