diff --git a/src/patch/peripheral.rs b/src/patch/peripheral.rs
index 2935aa4..8a16820 100644
--- a/src/patch/peripheral.rs
+++ b/src/patch/peripheral.rs
@@ -247,9 +247,11 @@ pub(crate) trait RegisterBlockExt: Name {
     /// Remove fields from rname and mark it as derivedFrom rderive.
     /// Update all derivedFrom referencing rname
     fn derive_register(&mut self, rspec: &str, rderive: &Yaml, bpath: &BlockPath) -> PatchResult {
-        let (rderive, info) = if let Some(rderive) = rderive.as_str() {
+        let (rspec, ignore) = rspec.spec();
+        let (rderive, dim, info) = if let Some(rderive) = rderive.as_str() {
             (
                 rderive,
+                None,
                 RegisterInfo::builder().derived_from(Some(rderive.into())),
             )
         } else if let Some(hash) = rderive.as_hash() {
@@ -258,6 +260,7 @@ pub(crate) trait RegisterBlockExt: Name {
             })?;
             (
                 rderive,
+                make_dim_element(hash)?,
                 make_register(hash, Some(bpath))?.derived_from(Some(rderive.into())),
             )
         } else {
@@ -277,15 +280,24 @@ pub(crate) trait RegisterBlockExt: Name {
             })?;
         }
 
+        let rtags = self.iter_registers(rspec).collect::<Vec<_>>();
         let mut found = Vec::new();
-        for register in self.iter_registers(rspec) {
-            found.push(register.name.to_string());
-            register.modify_from(info.clone(), VAL_LVL)?;
-        }
-        if found.is_empty() {
+        if !rtags.is_empty() {
+            for rtag in rtags {
+                found.push(rtag.name.to_string());
+                modify_dim_element(rtag, &dim)?;
+                rtag.modify_from(info.clone(), VAL_LVL)?;
+            }
+        } else if !ignore {
             super::check_dimable_name(rspec)?;
-            let register = info.name(rspec.into()).build(VAL_LVL)?.single();
-            self.add_child(RegisterCluster::Register(register));
+            let reg = info.name(rspec.into()).build(VAL_LVL)?;
+            self.add_child(RegisterCluster::Register({
+                if let Some(dim) = dim {
+                    reg.array(dim.build(VAL_LVL)?)
+                } else {
+                    reg.single()
+                }
+            }));
         }
         for rname in found {
             for r in self
diff --git a/src/patch/register.rs b/src/patch/register.rs
index 7552d3a..cd85e4c 100644
--- a/src/patch/register.rs
+++ b/src/patch/register.rs
@@ -289,10 +289,16 @@ impl RegisterExt for Register {
     }
 
     fn modify_field(&mut self, fspec: &str, fmod: &Hash, rpath: &RegisterPath) -> PatchResult {
+        let (fspec, ignore) = fspec.spec();
         let ftags = self.iter_fields(fspec).collect::<Vec<_>>();
         let field_builder = make_field(fmod, Some(rpath))?;
         let dim = make_dim_element(fmod)?;
-        if !ftags.is_empty() {
+        if ftags.is_empty() && !ignore {
+            let present = self.present_fields();
+            return Err(anyhow!(
+                "Could not find `{rpath}:{fspec}. Present fields: {present}.`"
+            ));
+        } else {
             for ftag in ftags {
                 modify_dim_element(ftag, &dim)?;
                 if let Some(value) = fmod
@@ -362,28 +368,39 @@ impl RegisterExt for Register {
                 dpath.into()
             }
         }
-        let info = if let Some(dpath) = fderive.as_str() {
-            FieldInfo::builder().derived_from(Some(make_path(dpath, rpath)))
+        let (fspec, ignore) = fspec.spec();
+        let (dim, info) = if let Some(dpath) = fderive.as_str() {
+            (
+                None,
+                FieldInfo::builder().derived_from(Some(make_path(dpath, rpath))),
+            )
         } else if let Some(hash) = fderive.as_hash() {
             let dpath = hash.get_str("_from")?.ok_or_else(|| {
                 anyhow!("derive: source field not given, please add a _from field to {fspec}")
             })?;
-            make_field(hash, Some(rpath))?.derived_from(Some(make_path(dpath, rpath)))
+            (
+                make_dim_element(hash)?,
+                make_field(hash, Some(rpath))?.derived_from(Some(make_path(dpath, rpath))),
+            )
         } else {
             return Err(anyhow!("derive: incorrect syntax for {fspec}"));
         };
-
-        let mut found = false;
-        for field in self.iter_fields(fspec) {
-            found = true;
-            field.modify_from(info.clone(), VAL_LVL)?;
-        }
-        if !found {
-            {
-                super::check_dimable_name(fspec)?;
-                let field = info.name(fspec.into()).build(VAL_LVL)?.single();
-                self.fields.get_or_insert(Vec::new()).push(field);
-            }
+        let ftags = self.iter_fields(fspec).collect::<Vec<_>>();
+        if !ftags.is_empty() {
+            for ftag in ftags {
+                modify_dim_element(ftag, &dim)?;
+                ftag.modify_from(info.clone(), VAL_LVL)?;
+            }
+        } else if !ignore {
+            super::check_dimable_name(fspec)?;
+            let field = info.name(fspec.into()).build(VAL_LVL)?;
+            self.fields.get_or_insert(Vec::new()).push({
+                if let Some(dim) = dim {
+                    field.array(dim.build(VAL_LVL)?)
+                } else {
+                    field.single()
+                }
+            });
         }
         Ok(())
     }