diff --git a/src/arch/x86_64/CodeGen.zig b/src/arch/x86_64/CodeGen.zig
index 45d73a4180..bc0171899a 100644
--- a/src/arch/x86_64/CodeGen.zig
+++ b/src/arch/x86_64/CodeGen.zig
@@ -3254,6 +3254,7 @@ fn genBinMathOpMir(self: *Self, mir_tag: Mir.Inst.Tag, dst_ty: Type, dst_mcv: MC
 
 // Performs integer multiplication between dst_mcv and src_mcv, storing the result in dst_mcv.
 fn genIMulOpMir(self: *Self, dst_ty: Type, dst_mcv: MCValue, src_mcv: MCValue) !void {
+    const abi_size = @intCast(u32, dst_ty.abiSize(self.target.*));
     switch (dst_mcv) {
         .none => unreachable,
         .undef => unreachable,
@@ -3276,8 +3277,8 @@ fn genIMulOpMir(self: *Self, dst_ty: Type, dst_mcv: MCValue, src_mcv: MCValue) !
                     _ = try self.addInst(.{
                         .tag = .imul_complex,
                         .ops = (Mir.Ops{
-                            .reg1 = registerAlias(dst_reg, @divExact(src_reg.size(), 8)),
-                            .reg2 = src_reg,
+                            .reg1 = registerAlias(dst_reg, abi_size),
+                            .reg2 = registerAlias(src_reg, abi_size),
                         }).encode(),
                         .data = undefined,
                     });
@@ -3305,7 +3306,7 @@ fn genIMulOpMir(self: *Self, dst_ty: Type, dst_mcv: MCValue, src_mcv: MCValue) !
                     _ = try self.addInst(.{
                         .tag = .imul_complex,
                         .ops = (Mir.Ops{
-                            .reg1 = registerAlias(dst_reg, @intCast(u32, dst_ty.abiSize(self.target.*))),
+                            .reg1 = registerAlias(dst_reg, abi_size),
                             .reg2 = .rbp,
                             .flags = 0b01,
                         }).encode(),
@@ -3342,8 +3343,8 @@ fn genIMulOpMir(self: *Self, dst_ty: Type, dst_mcv: MCValue, src_mcv: MCValue) !
                     _ = try self.addInst(.{
                         .tag = .imul_complex,
                         .ops = (Mir.Ops{
-                            .reg1 = registerAlias(dst_reg, @divExact(src_reg.size(), 8)),
-                            .reg2 = src_reg,
+                            .reg1 = registerAlias(dst_reg, abi_size),
+                            .reg2 = registerAlias(src_reg, abi_size),
                         }).encode(),
                         .data = undefined,
                     });
diff --git a/test/behavior/math.zig b/test/behavior/math.zig
index 3abbece353..314d52be66 100644
--- a/test/behavior/math.zig
+++ b/test/behavior/math.zig
@@ -639,7 +639,6 @@ test "128-bit multiplication" {
 
 test "@addWithOverflow" {
     if (builtin.zig_backend == .stage2_c) return error.SkipZigTest; // TODO
-    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
 
@@ -684,7 +683,6 @@ test "small int addition" {
 
 test "@mulWithOverflow" {
     if (builtin.zig_backend == .stage2_c) return error.SkipZigTest; // TODO
-    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
 
@@ -698,14 +696,16 @@ test "@mulWithOverflow" {
     var b: u8 = 2;
     try expect(!@mulWithOverflow(u8, a, b, &result));
     try expect(result == 246);
-    b = 4;
-    try expect(@mulWithOverflow(u8, a, b, &result));
-    try expect(result == 236);
+
+    if (builtin.zig_backend != .stage2_x86_64) { // TODO fix mul/imul on x86_64
+        b = 4;
+        try expect(@mulWithOverflow(u8, a, b, &result));
+        try expect(result == 236);
+    }
 }
 
 test "@subWithOverflow" {
     if (builtin.zig_backend == .stage2_c) return error.SkipZigTest; // TODO
-    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
 
@@ -747,7 +747,6 @@ test "@shlWithOverflow" {
 
 test "overflow arithmetic with u0 values" {
     if (builtin.zig_backend == .stage2_c) return error.SkipZigTest; // TODO
-    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest; // TODO
 
     var result: u0 = undefined;
     try expect(!@addWithOverflow(u0, 0, 0, &result));