diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index a4eccf0..2dbf922 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -96,6 +96,13 @@
           # exit with an error code and list the missing entries.
           make -f ci/unlisted.make
 
+      - name: Check hlgroups (are any new hlgroups added, but not handled in highlight.c)
+        run: |
+          # If any highlight groups have been documented, but not handled in
+          # highlight.c, nor listed as 'intentionally left out' in hlgroups.ignore,
+          # exit with an error code and list the missing entries.
+          make -C ci -f hlgroups.make
+
       - run: sudo dpkg --add-architecture i386
         if: matrix.architecture == 'i386'
 
diff --git a/Filelist b/Filelist
index 22a987c..07560e5 100644
--- a/Filelist
+++ b/Filelist
@@ -1148,6 +1148,8 @@
 		.github/workflows/label.yml \
 		SECURITY.md \
 		ci/unlisted.make \
+		ci/hlgroups.make \
+		ci/hlgroups.ignore \
 		src/libvterm/CODE-MAP \
 		runtime/syntax/testdir/input/html_html \
 
diff --git a/ci/hlgroups.ignore b/ci/hlgroups.ignore
new file mode 100644
index 0000000..41e06f1
--- /dev/null
+++ b/ci/hlgroups.ignore
@@ -0,0 +1,66 @@
+ColorColumn
+ComplMatchIns
+Conceal
+Cursor
+CursorColumn
+CursorIM
+CursorLine
+CursorLineNr
+debugBreakpoint
+debugPC
+DiffAdd
+DiffChange
+DiffDelete
+DiffText
+Directory
+ErrorMsg
+FoldColumn
+Folded
+Ignore
+IncSearch
+lCursor
+LineNr
+LineNrAbove
+LineNrBelow
+MatchParen
+Menu
+ModeMsg
+MoreMsg
+MsgArea
+NonText
+Normal
+Pmenu
+PmenuSbar
+PmenuSel
+PmenuThumb
+Question
+Scrollbar
+Search
+SignColumn
+SpecialKey
+SpellBad
+SpellCap
+SpellLocal
+SpellRare
+StatusLine
+StatusLineNC
+StatusLineTerm
+StatusLineTermNC
+TabLine
+TabLineFill
+TabLineSel
+Terminal
+Title
+TOhtmlProgress
+TOhtml-progress-color
+ToolbarButton
+ToolbarLine
+Tooltip
+User1
+User1..9
+User9
+VertSplit
+Visual
+VisualNOS
+WarningMsg
+WildMenu
diff --git a/ci/hlgroups.make b/ci/hlgroups.make
new file mode 100644
index 0000000..65b39a8
--- /dev/null
+++ b/ci/hlgroups.make
@@ -0,0 +1,18 @@
+# vim: ft=make
+SHELL = /bin/bash
+
+# Default target to actually run the comparison:
+.PHONY: check
+.INTERMEDIATE: hlgroups deflinks hlgroups.stripped
+
+check: hlgroups.stripped deflinks
+	diff hlgroups.stripped deflinks
+
+hlgroups:
+	grep '\*hl-' ../runtime/doc/*txt | sed -E -e 's/.*:<?\s*//' -e 's/hl-//g' -e 's/\*//g' -e 's/ /\n/g' | sort > hlgroups
+
+deflinks: ../src/highlight.c
+	grep '"default link'  $< | sed 's/.*default link\s*\(.*\)\s.*/\1/' | sort > deflinks
+
+hlgroups.stripped: hlgroups.ignore hlgroups
+	grep -v -x -F -f hlgroups.ignore hlgroups > hlgroups.stripped
diff --git a/ci/unlisted.make b/ci/unlisted.make
index 04dfcb5..6d506eb 100644
--- a/ci/unlisted.make
+++ b/ci/unlisted.make
@@ -21,7 +21,7 @@
 			p; \
 		}'))
 
-# In Makefile's `prepeare` target, all the IN_README_DIR files are moved from
+# In Makefile's `prepare` target, all the IN_README_DIR files are moved from
 # READMEdir to the root, so add those files in their Git-tracked location:
 all_patterns := $(all_patterns) \
 	$(foreach readme, $(IN_README_DIR), READMEdir/$(readme))