diff --git a/src/ast.rs b/src/ast.rs
index f12dfb6..63a7cf9 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -117,7 +117,8 @@ impl PredicateDeclaration
 		let dependencies = match *dependencies
 		{
 			Some(ref dependencies) => dependencies,
-			None => unreachable!("all dependencies should have been collected at this point"),
+			// Input predicates don’t have completed definitions and no dependencies, so ignore them
+			None => return,
 		};
 
 		for dependency in dependencies.iter()
diff --git a/src/problem.rs b/src/problem.rs
index e482272..e1f550c 100644
--- a/src/problem.rs
+++ b/src/problem.rs
@@ -69,6 +69,11 @@ impl Problem
 				continue;
 			}
 
+			if *predicate_declaration.is_input.borrow()
+			{
+				continue;
+			}
+
 			let matching_statement = |statement: &&Statement|
 				match statement.kind
 				{