diff --git a/io.c b/io.c
index 6038609..01a7a4a 100644
--- a/io.c
+++ b/io.c
@@ -2366,12 +2366,27 @@ rb_io_set_nonblock(rb_io_t *fptr)
 void
 rb_readwrite_sys_fail(int writable, const char *mesg);
 
+struct read_internal_arg {
+    int fd;
+    char *str_ptr;
+    long len;
+};
+
+static VALUE
+read_internal_call(VALUE arg)
+{
+    struct read_internal_arg *p = (struct read_internal_arg *)arg;
+    p->len = rb_read_internal(p->fd, p->str_ptr, p->len);
+    return Qundef;
+}
+
 static VALUE
 io_getpartial(int argc, VALUE *argv, VALUE io, int nonblock)
 {
     rb_io_t *fptr;
     VALUE length, str;
     long n, len;
+    struct read_internal_arg arg;
 
     rb_scan_args(argc, argv, "11", &length, &str);
 
@@ -2398,8 +2413,11 @@ io_getpartial(int argc, VALUE *argv, VALUE io, int nonblock)
         }
 	io_setstrbuf(&str, len);
 	rb_str_locktmp(str);
-	n = rb_read_internal(fptr->fd, RSTRING_PTR(str), len);
-	rb_str_unlocktmp(str);
+	arg.fd = fptr->fd;
+	arg.str_ptr = RSTRING_PTR(str);
+	arg.len = len;
+	rb_ensure(read_internal_call, (VALUE)&arg, rb_str_unlocktmp, str);
+	n = arg.len;
         if (n < 0) {
             if (!nonblock && rb_io_wait_readable(fptr->fd))
                 goto again;
@@ -4511,6 +4529,7 @@ rb_io_sysread(int argc, VALUE *argv, VALUE io)
     VALUE len, str;
     rb_io_t *fptr;
     long n, ilen;
+    struct read_internal_arg arg;
 
     rb_scan_args(argc, argv, "11", &len, &str);
     ilen = NUM2LONG(len);
@@ -4540,8 +4559,11 @@ rb_io_sysread(int argc, VALUE *argv, VALUE io)
 
     io_setstrbuf(&str, ilen);
     rb_str_locktmp(str);
-    n = rb_read_internal(fptr->fd, RSTRING_PTR(str), ilen);
-    rb_str_unlocktmp(str);
+    arg.fd = fptr->fd;
+    arg.str_ptr = RSTRING_PTR(str);
+    arg.len = ilen;
+    rb_ensure(read_internal_call, (VALUE)&arg, rb_str_unlocktmp, str);
+    n = arg.len;
 
     if (n == -1) {
 	rb_sys_fail_path(fptr->pathv);