diff --git a/src/ops.c b/src/ops.c
index 2a62506..72ffd56 100644
--- a/src/ops.c
+++ b/src/ops.c
@@ -2001,7 +2001,7 @@
 	{
 	    curr = skipwhite(curr);
 	    if (*curr != NUL && *curr != ')'
-		    && currsize != 0 && endcurr1 != TAB
+		    && sumsize != 0 && endcurr1 != TAB
 		    && (!has_format_option(FO_MBYTE_JOIN)
 			|| (mb_ptr2char(curr) < 0x100 && endcurr1 < 0x100))
 		    && (!has_format_option(FO_MBYTE_JOIN2)
diff --git a/src/testdir/test_join.vim b/src/testdir/test_join.vim
index 5801c2f..377edab 100644
--- a/src/testdir/test_join.vim
+++ b/src/testdir/test_join.vim
@@ -427,3 +427,14 @@
   call assert_equal(expected, getline(1, '$'))
   close!
 endfunc
+
+func Test_join_lines()
+  new
+  call setline(1, ['a', 'b', '', 'c', 'd'])
+  %join
+  call assert_equal('a b c d', getline(1))
+  call setline(1, ['a', 'b', '', 'c', 'd'])
+  normal 5J
+  call assert_equal('a b c d', getline(1))
+  bwipe!
+endfunc
diff --git a/src/version.c b/src/version.c
index c11710a..65924cd 100644
--- a/src/version.c
+++ b/src/version.c
@@ -743,6 +743,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    18,
+/**/
     17,
 /**/
     16,