diff --git a/src/mir/builder/control_flow.rs b/src/mir/builder/control_flow.rs
index 3c06d701..0a3d6cd6 100644
--- a/src/mir/builder/control_flow.rs
+++ b/src/mir/builder/control_flow.rs
@@ -402,14 +402,20 @@ impl super::MirBuilder {
         let mut function_entry_map: HashMap<String, BasicBlockId> = HashMap::new();
 
         // 1. Allocate new block IDs for ALL functions (Phase 189)
+        // DETERMINISM FIX: Sort functions by name to ensure consistent iteration order
         if debug {
             eprintln!("[cf_loop/joinir] Phase 189: Allocating block IDs for all functions");
         }
-        for (func_name, func) in &mir_module.functions {
+        let mut functions: Vec<_> = mir_module.functions.iter().collect();
+        functions.sort_by_key(|(name, _)| name.as_str());
+        for (func_name, func) in functions {
             if debug {
                 eprintln!("[cf_loop/joinir]   Function: {}", func_name);
             }
-            for old_block_id in func.blocks.keys() {
+            // DETERMINISM FIX: Sort blocks by ID to ensure consistent iteration order
+            let mut blocks: Vec<_> = func.blocks.iter().collect();
+            blocks.sort_by_key(|(id, _)| id.0);
+            for (old_block_id, _) in blocks {
                 let new_block_id = self.block_gen.next();
                 // Use composite key to avoid collision between functions
                 block_map.insert((func_name.clone(), *old_block_id), new_block_id);
@@ -485,11 +491,14 @@ impl super::MirBuilder {
         }
 
         // 5. Merge ALL functions (Phase 189: iterate over all, not just first)
+        // DETERMINISM FIX: Sort functions by name to ensure consistent iteration order
         if debug {
             eprintln!("[cf_loop/joinir] Phase 189: Merging {} functions", mir_module.functions.len());
         }
         // Phase 189: Iterate over both names and functions (need name for composite keys)
-        for (func_name, func) in &mir_module.functions {
+        let mut functions_merge: Vec<_> = mir_module.functions.iter().collect();
+        functions_merge.sort_by_key(|(name, _)| name.as_str());
+        for (func_name, func) in functions_merge {
             if debug {
                 eprintln!(
                     "[cf_loop/joinir]   Merging function '{}' with {} blocks, entry={:?}",
@@ -507,7 +516,10 @@ impl super::MirBuilder {
             }
 
             // Clone and remap all blocks from this function
-            for (old_block_id, old_block) in &func.blocks {
+            // DETERMINISM FIX: Sort blocks by ID to ensure consistent iteration order
+            let mut blocks_merge: Vec<_> = func.blocks.iter().collect();
+            blocks_merge.sort_by_key(|(id, _)| id.0);
+            for (old_block_id, old_block) in blocks_merge {
                 // Use composite key to get correct mapping for this function's block
                 let new_block_id = block_map[&(func_name.clone(), *old_block_id)];
                 let mut new_block = BasicBlock::new(new_block_id);