diff --git a/src/testdir/test_quickfix.vim b/src/testdir/test_quickfix.vim
index 33ce700..c784a2d 100644
--- a/src/testdir/test_quickfix.vim
+++ b/src/testdir/test_quickfix.vim
@@ -6447,4 +6447,53 @@
   call setqflist([], 'f')
 endfunc
 
+" Test for "%b" in "errorformat"
+func Test_efm_format_b()
+  call setqflist([], 'f')
+  new
+  call setline(1, ['1: abc', '1: def', '1: ghi'])
+  let b1 = bufnr()
+  new
+  call setline(1, ['2: abc', '2: def', '2: ghi'])
+  let b2 = bufnr()
+  new
+  call setline(1, ['3: abc', '3: def', '3: ghi'])
+  let b3 = bufnr()
+  new
+  let lines =<< trim eval END
+    {b1}:1:1
+    {b2}:2:2
+    {b3}:3:3
+  END
+  call setqflist([], ' ', #{lines: lines, efm: '%b:%l:%c'})
+  cfirst
+  call assert_equal([b1, 1, 1], [bufnr(), line('.'), col('.')])
+  cnext
+  call assert_equal([b2, 2, 2], [bufnr(), line('.'), col('.')])
+  cnext
+  call assert_equal([b3, 3, 3], [bufnr(), line('.'), col('.')])
+  enew!
+
+  " Use a non-existing buffer
+  let lines =<< trim eval END
+    9991:1:1:m1
+    9992:2:2:m2
+    {b3}:3:3:m3
+  END
+  call setqflist([], ' ', #{lines: lines, efm: '%b:%l:%c:%m'})
+  cfirst | cnext
+  call assert_equal([b3, 3, 3], [bufnr(), line('.'), col('.')])
+  " Lines with non-existing buffer numbers should be used as non-error lines
+  call assert_equal([
+    \ #{lnum: 0, bufnr: 0, end_lnum: 0, pattern: '', valid: 0, vcol: 0, nr: -1,
+    \   module: '', type: '', end_col: 0, col: 0, text: '9991:1:1:m1'},
+    \ #{lnum: 0, bufnr: 0, end_lnum: 0, pattern: '', valid: 0, vcol: 0, nr: -1,
+    \   module: '', type: '', end_col: 0, col: 0, text: '9992:2:2:m2'},
+    \ #{lnum: 3, bufnr: b3, end_lnum: 0, pattern: '', valid: 1, vcol: 0,
+    \   nr: -1, module: '', type: '', end_col: 0, col: 3, text: 'm3'}],
+    \ getqflist())
+  %bw!
+  call setqflist([], 'f')
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab