diff --git a/mlkem/src/fips202/native/x86_64/src/keccak_f1600_x4_avx2_asm.S b/mlkem/src/fips202/native/x86_64/src/keccak_f1600_x4_avx2_asm.S
index 145a230f17..24365a7177 100644
--- a/mlkem/src/fips202/native/x86_64/src/keccak_f1600_x4_avx2_asm.S
+++ b/mlkem/src/fips202/native/x86_64/src/keccak_f1600_x4_avx2_asm.S
@@ -18,7 +18,11 @@
 MLK_ASM_FN_SYMBOL(keccak_f1600_x4_avx2_asm)
 
         .cfi_startproc
-        subq $0x300, %rsp            # imm = 0x300
+        pushq %rbp
+        .cfi_adjust_cfa_offset 8
+        movq %rsp, %rbp
+        subq $0x300, %rsp
+        andq $-32, %rsp
         .cfi_adjust_cfa_offset 0x300
         vmovdqu (%rdi), %ymm0
         vmovdqu 0xc8(%rdi), %ymm3
@@ -437,8 +441,10 @@ LLkeccak_f1600_x4_avx2:
         vmovhpd %xmm3, 0x188(%rdi)
         vmovq %xmm15, 0x250(%rdi)
         vmovhpd %xmm15, 0x318(%rdi)
-        addq $0x300, %rsp            # imm = 0x300
+        movq %rbp, %rsp
         .cfi_adjust_cfa_offset -0x300
+        popq %rbp
+        .cfi_adjust_cfa_offset -8
         retq
         .cfi_endproc
 
diff --git a/mlkem/src/native/x86_64/src/rej_uniform_avx2_asm.S b/mlkem/src/native/x86_64/src/rej_uniform_avx2_asm.S
index 36b471b1dd..8bc7c48f0d 100644
--- a/mlkem/src/native/x86_64/src/rej_uniform_avx2_asm.S
+++ b/mlkem/src/native/x86_64/src/rej_uniform_avx2_asm.S
@@ -34,7 +34,11 @@
 MLK_ASM_FN_SYMBOL(rej_uniform_avx2_asm)
 
         .cfi_startproc
-        subq $0x210, %rsp            # imm = 0x210
+        pushq %rbp
+        .cfi_adjust_cfa_offset 8
+        movq %rsp, %rbp
+        subq $0x210, %rsp
+        andq $-32, %rsp
         .cfi_adjust_cfa_offset 0x210
         xorl %eax, %eax
         testq %rdx, %rdx
@@ -88,8 +92,10 @@ Lrej_uniform_asm_final_copy:
         rep  movsb (%rsi), %es:(%rdi)
 
 Lrej_uniform_asm_end:
-        addq $0x210, %rsp            # imm = 0x210
+        movq %rbp, %rsp
         .cfi_adjust_cfa_offset -0x210
+        popq %rbp
+        .cfi_adjust_cfa_offset -8
         retq
         .cfi_endproc