diff --git a/src/python/jw/pkg/App.py b/src/python/jw/pkg/App.py
index d5480a7a..af9b9311 100644
--- a/src/python/jw/pkg/App.py
+++ b/src/python/jw/pkg/App.py
@@ -210,6 +210,7 @@ class App(Base):
         names_only: bool,
     ) -> None:
         name = self.strip_module_from_spec(spec)
+        mod = re.split('([=><]+)', spec)[0].strip()
         if names_only:
             spec = name
         if spec in buf:
@@ -219,6 +220,15 @@ class App(Base):
                 buf.append(spec)
             return
         visited.add(spec)
+        needed_subpackage = 'devel' if mod.endswith(('-dev', '-devel')) else 'run'
+        if not self.is_installed(name, devel = True):
+            if not mod.endswith(('-dev', '-devel')):
+                if self.is_installed(name, devel = False):
+                    return
+            raise Exception(
+                f'Unmet dependency on {mod}: the -{needed_subpackage} package '
+                f'of project {name} is not installed'
+            )
         vals = self.get_value(name, section, key)
         log(
             DEBUG,