diff --git a/proxmox-api-macro/src/api.rs b/proxmox-api-macro/src/api.rs
index 4f511807..ef3e6102 100644
--- a/proxmox-api-macro/src/api.rs
+++ b/proxmox-api-macro/src/api.rs
@@ -47,7 +47,7 @@ pub struct Schema {
     pub description: Option<syn::LitStr>,
 
     /// The specific schema type (Object, String, ...)
-    item: SchemaItem,
+    pub item: SchemaItem,
 
     /// The remaining key-value pairs the `SchemaItem` parser did not extract will be appended as
     /// builder-pattern method calls to this schema.
@@ -100,6 +100,15 @@ impl TryFrom<JSONObject> for Schema {
 }
 
 impl Schema {
+    fn blank(span: Span) -> Self {
+        Self {
+            span,
+            description: None,
+            item: SchemaItem::Inferred(span),
+            properties: Vec::new(),
+        }
+    }
+
     fn to_typed_schema(&self, ts: &mut TokenStream) -> Result<(), Error> {
         self.item.to_schema(
             ts,
@@ -148,7 +157,7 @@ impl Schema {
     }
 }
 
-enum SchemaItem {
+pub enum SchemaItem {
     Null,
     Boolean,
     Integer,
@@ -317,7 +326,7 @@ impl SchemaItem {
 
 #[derive(Default)]
 /// Contains a sorted list of properties:
-struct SchemaObject {
+pub struct SchemaObject {
     properties: Vec<(FieldName, bool, Schema)>,
 }
 
@@ -388,7 +397,7 @@ impl SchemaObject {
     }
 }
 
-struct SchemaArray {
+pub struct SchemaArray {
     item: Box<Schema>,
 }
 
diff --git a/proxmox-api-macro/src/api/method.rs b/proxmox-api-macro/src/api/method.rs
index 9c7240a7..6d809023 100644
--- a/proxmox-api-macro/src/api/method.rs
+++ b/proxmox-api-macro/src/api/method.rs
@@ -140,42 +140,14 @@ fn handle_function_signature(
         let (pat_type, pat) = check_input_type(input)?;
 
         // For any named type which exists on the function signature...
-        let schema: &mut Schema = if let Some((_ident, _optional, schema)) =
+        if let Some((_ident, _optional, ref mut schema)) =
             input_schema.find_obj_property_by_ident_mut(&pat.ident.to_string())
         {
-            match &mut schema.item {
-                // ... if it has no `type` property (item = SchemaItem::Inferred), get a mutable
-                // reference to the schema, so that we can...
-                SchemaItem::Inferred(_span) => schema,
-                // other types are fine:
-                _ => continue,
-            }
+            // try to infer the type in the schema if it is not specified explicitly:
+            util::infer_type(schema, &*pat_type.ty)?;
         } else {
             continue;
         };
-
-        // ... infer the type from the function parameters:
-        match &*pat_type.ty {
-            syn::Type::Path(path) if path.qself.is_none() => {
-                if path.path.is_ident("String") {
-                    schema.item = SchemaItem::String;
-                    continue;
-                } else if path.path.is_ident("bool") {
-                    schema.item = SchemaItem::Boolean;
-                    continue;
-                } else if super::INTNAMES.iter().any(|n| path.path.is_ident(n)) {
-                    schema.item = SchemaItem::Integer;
-                    continue;
-                } else if super::NUMBERNAMES.iter().any(|n| path.path.is_ident(n)) {
-                    schema.item = SchemaItem::Number;
-                    continue;
-                }
-            }
-            _ => (),
-        }
-
-        // if we can't, bail out:
-        bail!(&pat_type.ty => "cannot infer parameter type from this rust type");
     }
 
     for input in sig.inputs.iter() {
diff --git a/proxmox-api-macro/src/util.rs b/proxmox-api-macro/src/util.rs
index 588739fa..bcd20c79 100644
--- a/proxmox-api-macro/src/util.rs
+++ b/proxmox-api-macro/src/util.rs
@@ -10,7 +10,7 @@ use syn::Token;
 
 use failure::Error;
 
-use crate::api::Schema;
+use crate::api::{self, Schema, SchemaItem};
 
 /// A more relaxed version of Ident which allows hyphens.
 ///
@@ -441,3 +441,31 @@ pub fn derive_descriptions(
 
     Ok(())
 }
+
+pub fn infer_type(schema: &mut Schema, ty: &syn::Type) -> Result<(), Error> {
+    if let SchemaItem::Inferred(_) = schema.item {
+        //
+    } else {
+        return Ok(());
+    }
+
+    // infer the type from a rust type:
+    match ty {
+        syn::Type::Path(path) if path.qself.is_none() => {
+            if path.path.is_ident("String") {
+                schema.item = SchemaItem::String;
+            } else if path.path.is_ident("bool") {
+                schema.item = SchemaItem::Boolean;
+            } else if api::INTNAMES.iter().any(|n| path.path.is_ident(n)) {
+                schema.item = SchemaItem::Integer;
+            } else if api::NUMBERNAMES.iter().any(|n| path.path.is_ident(n)) {
+                schema.item = SchemaItem::Number;
+            } else {
+                bail!(ty => "cannot infer parameter type from this rust type");
+            }
+        }
+        _ => (),
+    }
+
+    Ok(())
+}