diff --git a/techtree-manager/src/collect.rs b/techtree-manager/src/collect.rs
index c0034ed..b02afca 100644
--- a/techtree-manager/src/collect.rs
+++ b/techtree-manager/src/collect.rs
@@ -68,6 +68,21 @@ pub async fn collect_tree(ctx: &crate::Context) -> anyhow::Result<crate::tree::T
             .with_context(|| format!("Failed to fetch issue dependencies for #{issue}",))?;
 
         for dep in dependencies {
+            // Check that the dependency is actually an issue in the techtree and not external
+            let dep_repo = dep
+                .repository
+                .context("Dependency issue without repository info")?;
+            if dep_repo.owner.as_ref() != Some(&ctx.owner)
+                || dep_repo.name.as_ref() != Some(&ctx.repo)
+            {
+                log::warn!(
+                    "Issue #{issue} depends on external {}#{}, ignoring.",
+                    dep_repo.full_name.as_deref().unwrap_or("unknown?"),
+                    dep.number.unwrap_or(9999)
+                );
+                continue;
+            }
+
             let dep_number = dep.number.context("Missing issue number in dependency")?;
             if !tree.find_element_by_issue_number(dep_number).is_some() {
                 log::warn!("Found dependency from #{issue} on non-tracked issue #{dep_number}!");