diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
index 032478614c..7580e46367 100644
--- a/target/arm/translate-a64.c
+++ b/target/arm/translate-a64.c
@@ -7422,7 +7422,7 @@ static void handle_simd_dupe(DisasContext *s, int is_q, int rd, int rn,
                              int imm5)
 {
     int size = ctz32(imm5);
-    int index = imm5 >> (size + 1);
+    int index;
 
     if (size > 3 || (size == 3 && !is_q)) {
         unallocated_encoding(s);
@@ -7433,6 +7433,7 @@ static void handle_simd_dupe(DisasContext *s, int is_q, int rd, int rn,
         return;
     }
 
+    index = imm5 >> (size + 1);
     tcg_gen_gvec_dup_mem(size, vec_full_reg_offset(s, rd),
                          vec_reg_offset(s, rn, index, size),
                          is_q ? 16 : 8, vec_full_reg_size(s));