1 files changed, 3 insertions, 0 deletions
diff --git a/graph/src/error.rs b/graph/src/error.rs
index bf2714b..ce45acc 100644
--- a/graph/src/error.rs
+++ b/graph/src/error.rs
@@ -18,6 +18,8 @@ pub enum Error {
     /// The graph does not permit duplicate edges but encounters a
     /// repeated edge.
     DuplicatedEdge(usize, usize),
+    /// The source node has no room to add a new edge.
+    FullNode(usize),
 }
 
 impl Display for Error {
@@ -35,6 +37,7 @@ impl Display for Error {
                     "No duplicate edges permitted, but found one from {source} to {target}"
                 )
             }
+            Error::FullNode(index) => write!(f, "the node {index} has no room for new edges"),
         }
     }
 }