diff --git a/ext/java/org/jruby/ext/stringio/StringIO.java b/ext/java/org/jruby/ext/stringio/StringIO.java
index ce2e707..ed53fdd 100644
--- a/ext/java/org/jruby/ext/stringio/StringIO.java
+++ b/ext/java/org/jruby/ext/stringio/StringIO.java
@@ -1213,14 +1213,17 @@ private RubyString preadCommon(ThreadContext context, int argc, IRubyObject arg0
                 }
             case 2:
                 len = RubyNumeric.fix2int(arg0);
-                offset = RubyNumeric.fix2int(arg1);
                 if (!arg0.isNil()) {
-                    len = RubyNumeric.fix2int(arg0);
-
                     if (len < 0) {
                         throw runtime.newArgumentError("negative length " + len + " given");
                     }
                 }
+
+                offset = RubyNumeric.fix2int(arg1);
+                if (offset < 0) {
+                    throw runtime.newErrnoEINVALError("pread: Invalid offset argument");
+                }
+
                 break;
             default:
                 throw runtime.newArgumentError(argc, 0, 2);
@@ -1235,10 +1238,6 @@ private RubyString preadCommon(ThreadContext context, int argc, IRubyObject arg0
                 return (RubyString) str;
             }
 
-            if (offset < 0) {
-                throw runtime.newErrnoEINVALError("pread: Invalid offset argument");
-            }
-
             if (isOutside(offset)) {
                 throw context.runtime.newEOFError();
             }
diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index bde80b7..cd29875 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -161,6 +161,16 @@ strio_substr(struct StringIO *ptr, long pos, long len, rb_encoding *enc)
     return enc_subseq(str, pos, len, enc);
 }
 
+static VALUE
+strio_readbuf(struct StringIO *ptr, VALUE str)
+{
+    if (!NIL_P(str)) {
+	StringValue(str);
+	rb_str_modify(str);
+    }
+    return str;
+}
+
 #define StringIO(obj) get_strio(obj)
 #define StringIOForRead(obj) get_strio_for_read(obj)
 
@@ -1684,11 +1694,7 @@ strio_read(int argc, VALUE *argv, VALUE self)
 
     switch (argc) {
       case 2:
-	str = argv[1];
-	if (!NIL_P(str)) {
-	    StringValue(str);
-	    rb_str_modify(str);
-	}
+	str = strio_readbuf(ptr, argv[1]);
 	/* fall through */
       case 1:
 	if (!NIL_P(argv[0])) {
@@ -1753,6 +1759,8 @@ static VALUE
 strio_pread(int argc, VALUE *argv, VALUE self)
 {
     VALUE rb_len, rb_offset, rb_buf;
+    struct StringIO *ptr = readable(self);
+
     rb_scan_args(argc, argv, "21", &rb_len, &rb_offset, &rb_buf);
     long len = NUM2LONG(rb_len);
     long offset = NUM2LONG(rb_offset);
@@ -1761,6 +1769,12 @@ strio_pread(int argc, VALUE *argv, VALUE self)
 	rb_raise(rb_eArgError, "negative string size (or size too big): %" PRIsVALUE, rb_len);
     }
 
+    if (offset < 0) {
+	rb_syserr_fail_str(EINVAL, rb_sprintf("pread: Invalid offset argument: %" PRIsVALUE, rb_offset));
+    }
+
+    rb_buf = strio_readbuf(ptr, rb_buf);
+
     if (len == 0) {
 	if (NIL_P(rb_buf)) {
 	    return rb_str_new("", 0);
@@ -1768,12 +1782,6 @@ strio_pread(int argc, VALUE *argv, VALUE self)
 	return rb_buf;
     }
 
-    if (offset < 0) {
-	rb_syserr_fail_str(EINVAL, rb_sprintf("pread: Invalid offset argument: %" PRIsVALUE, rb_offset));
-    }
-
-    struct StringIO *ptr = readable(self);
-
     if (outside_p(ptr, offset)) {
 	rb_eof_error();
     }
diff --git a/test/stringio/test_stringio.rb b/test/stringio/test_stringio.rb
index 656c0bb..aca250a 100644
--- a/test/stringio/test_stringio.rb
+++ b/test/stringio/test_stringio.rb
@@ -831,9 +831,11 @@ def test_pread
     assert_raise(EOFError) { f.pread(1, 5) }
     assert_raise(ArgumentError) { f.pread(-1, 0) }
     assert_raise(Errno::EINVAL) { f.pread(3, -1) }
+    assert_raise(Errno::EINVAL) { f.pread(0, -1) }
+    assert_raise(IOError) { StringIO.new(nil, "w").pread(3, 0) }
+    assert_raise(TypeError) { f.pread(3, 0, []) }
 
     assert_equal "".b, StringIO.new("").pread(0, 0)
-    assert_equal "".b, StringIO.new("").pread(0, -10)
 
     buf = "stale".b
     assert_equal "stale".b, StringIO.new("").pread(0, 0, buf)