diff --git a/src/model/data_form.rs b/src/model/data_form.rs
index 91a9a75..57c3cd6 100644
--- a/src/model/data_form.rs
+++ b/src/model/data_form.rs
@@ -289,6 +289,27 @@ impl Requires for DataForm {
             .collect::<Vec<_>>();
         result.append(referenced_forms);
 
+        let sub_forms = &mut self
+            .entries
+            .entry
+            .iter()
+            .filter(|&entry| entry.get_type() == "subform")
+            .filter_map(|entry| match &entry.referenced_data_form {
+                Some(name) => Some(name),
+                None => None,
+            })
+            .collect::<HashSet<_>>()
+            .into_iter()
+            .map(|entry| match all.find_data_form(entry.as_str()) {
+                Some(contained) => Requirement::DataFormSubform(contained),
+                None => match all.find_unterformular(entry.as_str()) {
+                    Some(contained) => Requirement::UnterformularSubform(contained),
+                    None => Requirement::ExternalUnterformularSubform(entry.to_string()),
+                },
+            })
+            .collect::<Vec<_>>();
+        result.append(sub_forms);
+
         result
     }
 
@@ -331,6 +352,12 @@ impl Requires for DataForm {
                     | Requirement::ExternalUnterformularReference(_) => {
                         Some(format!("  > {}\n", entry.to_string()))
                     }
+                    Requirement::DataFormSubform(_)
+                    | Requirement::ExternalDataFormSubform(_)
+                    | Requirement::UnterformularSubform(_)
+                    | Requirement::ExternalUnterformularSubform(_) => {
+                        Some(format!("  $ {}\n", entry.to_string()))
+                    }
                     _ => None,
                 })
                 .filter(Option::is_some)
diff --git a/src/model/requirements.rs b/src/model/requirements.rs
index 7d10d97..cf6bcc1 100644
--- a/src/model/requirements.rs
+++ b/src/model/requirements.rs
@@ -40,6 +40,12 @@ pub enum Requirement<'a> {
     #[allow(dead_code)]
     ExternalDataFormReference(String),
     ExternalUnterformularReference(String),
+
+    DataFormSubform(&'a DataForm),
+    UnterformularSubform(&'a Unterformular),
+    #[allow(dead_code)]
+    ExternalDataFormSubform(String),
+    ExternalUnterformularSubform(String),
 }
 
 impl ToString for Requirement<'_> {
@@ -61,6 +67,14 @@ impl ToString for Requirement<'_> {
             Requirement::ExternalUnterformularReference(name) => {
                 format!("Unterformular (-) '{}' - hier nicht enthalten", name)
             }
+            Requirement::DataFormSubform(item) => item.to_listed_string(),
+            Requirement::UnterformularSubform(item) => item.to_listed_string(),
+            Requirement::ExternalDataFormSubform(name) => {
+                format!("Formular (-) '{}' - hier nicht enthalten", name)
+            }
+            Requirement::ExternalUnterformularSubform(name) => {
+                format!("Unterformular (-) '{}' - hier nicht enthalten", name)
+            }
         }
     }
 }
diff --git a/src/model/unterformular.rs b/src/model/unterformular.rs
index 999db19..823bd12 100644
--- a/src/model/unterformular.rs
+++ b/src/model/unterformular.rs
@@ -293,6 +293,27 @@ impl Requires for Unterformular {
             .collect::<Vec<_>>();
         result.append(referenced_forms);
 
+        let sub_forms = &mut self
+            .entries
+            .entry
+            .iter()
+            .filter(|&entry| entry.get_type() == "subform")
+            .filter_map(|entry| match &entry.referenced_data_form {
+                Some(name) => Some(name),
+                None => None,
+            })
+            .collect::<HashSet<_>>()
+            .into_iter()
+            .map(|entry| match all.find_data_form(entry.as_str()) {
+                Some(contained) => Requirement::DataFormSubform(contained),
+                None => match all.find_unterformular(entry.as_str()) {
+                    Some(contained) => Requirement::UnterformularSubform(contained),
+                    None => Requirement::ExternalUnterformularSubform(entry.to_string()),
+                },
+            })
+            .collect::<Vec<_>>();
+        result.append(sub_forms);
+
         result
     }
 
@@ -334,6 +355,12 @@ impl Requires for Unterformular {
                     | Requirement::ExternalUnterformularReference(_) => {
                         Some(format!("  > {}\n", entry.to_string()))
                     }
+                    Requirement::DataFormSubform(_)
+                    | Requirement::ExternalDataFormSubform(_)
+                    | Requirement::UnterformularSubform(_)
+                    | Requirement::ExternalUnterformularSubform(_) => {
+                        Some(format!("  $ {}\n", entry.to_string()))
+                    }
                     _ => None,
                 })
                 .filter(Option::is_some)