diff -Nur apt.orig/lib/puppet/provider/apt_key/apt_key.rb apt/lib/puppet/provider/apt_key/apt_key.rb
--- apt.orig/lib/puppet/provider/apt_key/apt_key.rb	2017-04-06 18:44:04.000000000 +0200
+++ apt/lib/puppet/provider/apt_key/apt_key.rb	2017-09-20 11:44:51.645966538 +0200
@@ -26,15 +26,25 @@
       key_output = apt_key(cli_args)
     end
 
-    pub_line, fpr_line = nil
+    pub_line, sub_line, fpr_line = nil
 
     key_array = key_output.split("\n").collect do |line|
       if line.start_with?('pub')
           pub_line = line
+          # reset fpr_line, to skip any previous subkeys which were collected
+          fpr_line = nil
+          sub_line = nil
+      elsif line.start_with?('sub')
+          sub_line = line
       elsif line.start_with?('fpr')
           fpr_line = line
       end
 
+      if (sub_line and fpr_line)
+        sub_line, fpr_line = nil
+        next
+      end
+
       next unless (pub_line and fpr_line)
 
       line_hash = key_line_hash(pub_line, fpr_line)
diff -Nur apt.orig/manifests/init.pp apt/manifests/init.pp
--- apt.orig/manifests/init.pp	2017-09-20 11:40:54.698483034 +0200
+++ apt/manifests/init.pp	2017-09-20 11:46:01.469814212 +0200
@@ -168,4 +168,19 @@
   if $pins {
     create_resources('apt::pin', $pins)
   }
+
+  # required for adding GPG keys on Debian 9 (and derivatives)
+  case $::operatingsystem {
+    'Debian': {
+      if versioncmp($::operatingsystemrelease, '9.0') >= 0 {
+        ensure_packages(['dirmngr'])
+      }
+    }
+    'Ubuntu': {
+      if versioncmp($::operatingsystemrelease, '17.04') >= 0 {
+        ensure_packages(['dirmngr'])
+      }
+    }
+    default: { }
+  }
 }
diff -Nur apt.orig/manifests/key.pp apt/manifests/key.pp
--- apt.orig/manifests/key.pp	2017-04-06 18:44:04.000000000 +0200
+++ apt/manifests/key.pp	2017-09-20 11:48:38.545471538 +0200
@@ -83,6 +83,24 @@
           options => $_options,
         }
         -> anchor { "apt_key ${_id} present": }
+
+        case $::operatingsystem {
+          'Debian': {
+            if versioncmp($::operatingsystemrelease, '9.0') >= 0 {
+              Apt::Key<| title == $title |> {
+                require => Package['dirmngr']
+              }
+            }
+          }
+          'Ubuntu': {
+            if versioncmp($::operatingsystemrelease, '17.04') >= 0 {
+              Apt::Key<| title == $title |> {
+                require => Package['dirmngr']
+              }
+            }
+          }
+          default: { }
+        }
       }
     }
 
diff -Nur apt.orig/metadata.json apt/metadata.json
--- apt.orig/metadata.json	2017-09-20 11:40:54.698483034 +0200
+++ apt/metadata.json	2017-09-20 11:50:20.257249670 +0200
@@ -17,7 +17,8 @@
       "operatingsystemrelease": [
         "6",
         "7",
-        "8"
+        "8",
+        "9"
       ]
     },
     {
@@ -26,7 +27,8 @@
         "10.04",
         "12.04",
         "14.04",
-        "16.04"
+        "16.04",
+        "17.04"
       ]
     }
   ],