diff --git a/src/ion/merge.rs b/src/ion/merge.rs
index b7a969e..1b04bd5 100644
--- a/src/ion/merge.rs
+++ b/src/ion/merge.rs
@@ -48,16 +48,16 @@ impl<'a, F: Function> Env<'a, F> {
             return false;
         }
 
-        #[cfg(debug)]
+        #[cfg(debug_assertions)]
         {
             // Sanity check: both bundles should contain only ranges with appropriate VReg classes.
             for entry in &self.bundles[from.index()].ranges {
                 let vreg = self.ranges[entry.index.index()].vreg;
-                assert_eq!(rc, self.vregs[vreg.index()].reg.class());
+                assert_eq!(from_rc, self.vreg_regs[vreg.index()].class());
             }
             for entry in &self.bundles[to.index()].ranges {
                 let vreg = self.ranges[entry.index.index()].vreg;
-                assert_eq!(rc, self.vregs[vreg.index()].reg.class());
+                assert_eq!(to_rc, self.vreg_regs[vreg.index()].class());
             }
         }
 
diff --git a/src/moves.rs b/src/moves.rs
index 25b1e81..2cb10e6 100644
--- a/src/moves.rs
+++ b/src/moves.rs
@@ -78,11 +78,11 @@ impl<T: Clone + Copy + Default> ParallelMoves<T> {
         // Sort moves by destination and check that each destination
         // has only one writer.
         self.parallel_moves.sort_by_key(|&(_, dst, _)| dst);
-        if cfg!(debug) {
+        if cfg!(debug_assertions) {
             let mut last_dst = None;
             for &(_, dst, _) in &self.parallel_moves {
                 if last_dst.is_some() {
-                    assert!(last_dst.unwrap() != dst);
+                    debug_assert!(last_dst.unwrap() != dst);
                 }
                 last_dst = Some(dst);
             }