diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 74bc87c491..fd7e324cd9 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -156,9 +156,11 @@ deps-debian:
     ## Build-time only dependencies
     - echo "RUN apt-get install -qq -y --no-install-recommends \\" >> Dockerfile
     - echo "appstream
+            bison
             ccache
             clang
             desktop-file-utils
+            flex
             gi-docgen
             git
             gobject-introspection
diff --git a/INSTALL.in b/INSTALL.in
index ab963d8862..f82a1f8e3d 100644
--- a/INSTALL.in
+++ b/INSTALL.in
@@ -282,10 +282,12 @@ help in that regard:
 
      Package Name        Version        Feature
 
+     bison               -              Image Map plug-in
      cairo-pdf           @CAIRO_PDF_REQUIRED_VERSION@         PDF export
      cfitsio             -              FITS
      iso-codes           -              Language selection
      ExcHndl             -              Crash logs on Windows with Dr. MinGW
+     flex                -              Image Map plug-in
      gs                  -              ghostscript
      libaa               -              ASCII art
      libheif             @LIBHEIF_REQUIRED_VERSION@         HEIF (HEIC, AVIF)