diff --git a/crates/engine/src/cmd/array.rs b/crates/engine/src/cmd/array.rs
index 839d71efc..1cc97a496 100644
--- a/crates/engine/src/cmd/array.rs
+++ b/crates/engine/src/cmd/array.rs
@@ -193,7 +193,19 @@ pub(crate) fn explode_array(d: &Drawing, e: &Entity) -> Option<Vec<Entity>> {
     let p = d.array_params(e)?;
     let blk = d.block(&ins.block)?;
     let m = ins.transform(blk.base.xy());
-    let mut out = Vec::new();
+    // Count first: a hostile array must be refused before any entity is cloned.
+    let total = blk
+        .entities
+        .iter()
+        .map(|it| match &it.kind {
+            EntityKind::Insert(i) if i.block.eq_ignore_ascii_case(&p.source) => d.block(&i.block).map_or(1, |b| b.entities.len()),
+            _ => 1,
+        })
+        .fold(0usize, usize::saturating_add);
+    if total > MAX_EXPLODED_OBJECTS {
+        return None;
+    }
+    let mut out = Vec::with_capacity(total);
     for item in blk.entities.iter() {
         let item = placed(e, item, &m);
         let source = match &item.kind {
@@ -202,9 +214,6 @@ pub(crate) fn explode_array(d: &Drawing, e: &Entity) -> Option<Vec<Entity>> {
         };
         match source {
             Some((im, b)) => {
-                if out.len().saturating_add(b.entities.len()) > MAX_EXPLODED_OBJECTS {
-                    return None;
-                }
                 out.extend(b.entities.iter().map(|se| placed(&item, se, &im)));
             }
             None => out.push(item),
diff --git a/crates/engine/src/cmd/blocks/extract.rs b/crates/engine/src/cmd/blocks/extract.rs
index 3e7707cc8..de85956c7 100644
--- a/crates/engine/src/cmd/blocks/extract.rs
+++ b/crates/engine/src/cmd/blocks/extract.rs
@@ -131,6 +131,7 @@ fn selected_tags(ents: &[std::sync::Arc<cadcraft_doc::Entity>], d: &Drawing, o:
             selected.push(tag);
         }
     };
+    let mut scanned = std::collections::HashSet::new();
     for entity in ents {
         let EntityKind::Insert(ins) = &entity.kind else { continue };
         let anonymous = ins.block.starts_with('*') || d.block(&ins.block).is_some_and(|b| b.anonymous);
@@ -140,9 +141,14 @@ fn selected_tags(ents: &[std::sync::Arc<cadcraft_doc::Entity>], d: &Drawing, o:
         for attribute in &ins.attribs {
             add(&attribute.tag);
         }
-        if let Some(block) = d.block(&ins.block) {
+        // A block's constants are read once, however many inserts reference it.
+        if scanned.insert(ins.block.as_str())
+            && let Some(block) = d.block(&ins.block)
+        {
             for entity in block.entities.iter() {
-                if let EntityKind::AttDef(attribute) = &entity.kind && attribute.constant {
+                if let EntityKind::AttDef(attribute) = &entity.kind
+                    && attribute.constant
+                {
                     add(&attribute.tag);
                 }
             }