diff --git a/yjit/src/backend/ir.rs b/yjit/src/backend/ir.rs
index 41842c9704..066e9dd4ce 100644
--- a/yjit/src/backend/ir.rs
+++ b/yjit/src/backend/ir.rs
@@ -567,7 +567,7 @@ impl Assembler
 
     /// Transform input instructions, consumes the input assembler
     pub(super) fn forward_pass<F>(mut self, mut map_insn: F) -> Assembler
-        where F: FnMut(&mut Assembler, usize, Op, Vec<Opnd>, Option<Target>, Option<String>, Option<PosMarkerFn>)
+        where F: FnMut(&mut Assembler, usize, Op, Vec<Opnd>, Option<Target>, Option<String>, Option<PosMarkerFn>, Vec<Opnd>)
     {
         let mut asm = Assembler {
             insns: Vec::default(),
@@ -594,6 +594,7 @@ impl Assembler
         }
 
         for (index, insn) in self.insns.drain(..).enumerate() {
+            let original_opnds = insn.opnds.clone();
             let opnds: Vec<Opnd> = insn.opnds.into_iter().map(|opnd| map_opnd(opnd, &mut indices)).collect();
 
             // For each instruction, either handle it here or allow the map_insn
@@ -603,7 +604,7 @@ impl Assembler
                     asm.comment(insn.text.unwrap().as_str());
                 },
                 _ => {
-                    map_insn(&mut asm, index, insn.op, opnds, insn.target, insn.text, insn.pos_marker);
+                    map_insn(&mut asm, index, insn.op, opnds, insn.target, insn.text, insn.pos_marker, original_opnds);
                 }
             };
 
@@ -664,7 +665,7 @@ impl Assembler
 
         let live_ranges: Vec<usize> = std::mem::take(&mut self.live_ranges);
 
-        let asm = self.forward_pass(|asm, index, op, opnds, target, text, pos_marker| {
+        let asm = self.forward_pass(|asm, index, op, opnds, target, text, pos_marker, original_insns| {
             // Check if this is the last instruction that uses an operand that
             // spans more than one instruction. In that case, return the
             // allocated register to the pool.
diff --git a/yjit/src/backend/x86_64/mod.rs b/yjit/src/backend/x86_64/mod.rs
index 7074c8980b..c3885be811 100644
--- a/yjit/src/backend/x86_64/mod.rs
+++ b/yjit/src/backend/x86_64/mod.rs
@@ -94,7 +94,7 @@ impl Assembler
     {
         let live_ranges: Vec<usize> = std::mem::take(&mut self.live_ranges);
 
-        self.forward_pass(|asm, index, op, opnds, target, text, pos_marker| {
+        self.forward_pass(|asm, index, op, opnds, target, text, pos_marker, original_opnds| {
             // Load heap object operands into registers because most
             // instructions can't directly work with 64-bit constants
             let opnds = match op {
@@ -134,7 +134,17 @@ impl Assembler
                             }
                         },
                         // Instruction output whose live range spans beyond this instruction
-                        (Opnd::InsnOut { idx, .. }, _) => {
+                        (Opnd::InsnOut { .. }, _) => {
+                            let idx = match original_opnds[0] {
+                                Opnd::InsnOut { idx, .. } => {
+                                    idx
+                                },
+                                _ => panic!("nooooo")
+                            };
+
+                            // Our input must be from a previous instruction!
+                            assert!(idx < index);
+
                             if live_ranges[idx] > index {
                                 (asm.load(opnds[0]), opnds[1])
                             } else {