diff --git a/cranelift/interpreter/src/step.rs b/cranelift/interpreter/src/step.rs
index 638db5937c..bfba030176 100644
--- a/cranelift/interpreter/src/step.rs
+++ b/cranelift/interpreter/src/step.rs
@@ -76,6 +76,16 @@ where
                     .as_slice();
                 DataValue::V128(buffer.try_into().expect("a 16-byte data buffer"))
             }
+            InstructionData::Shuffle { mask, .. } => {
+                let mask = state
+                    .get_current_function()
+                    .dfg
+                    .immediates
+                    .get(mask)
+                    .unwrap()
+                    .as_slice();
+                DataValue::V128(mask.try_into().expect("a 16-byte vector mask"))
+            }
             _ => inst.imm_value().unwrap(),
         })
     };
@@ -777,28 +787,18 @@ where
             ValueConversionKind::RoundNearestEven(ctrl_ty),
         )?),
         Opcode::Shuffle => {
-            if let InstructionData::Shuffle { mask, .. } = inst {
-                let mask = state
-                    .get_current_function()
-                    .dfg
-                    .immediates
-                    .get(mask)
-                    .unwrap()
-                    .as_slice();
-                let a = Value::into_array(&arg(0)?)?;
-                let b = Value::into_array(&arg(1)?)?;
-                let mut new = [0u8; 16];
-                for i in 0..mask.len() {
-                    if (mask[i] as usize) < a.len() {
-                        new[i] = a[mask[i] as usize];
-                    } else if (mask[i] as usize - a.len()) < b.len() {
-                        new[i] = b[mask[i] as usize - a.len()];
-                    } // else leave as 0.
-                }
-                assign(Value::vector(new, ctrl_ty)?)
-            } else {
-                unreachable!();
+            let mask = imm().into_array()?;
+            let a = Value::into_array(&arg(0)?)?;
+            let b = Value::into_array(&arg(1)?)?;
+            let mut new = [0u8; 16];
+            for i in 0..mask.len() {
+                if (mask[i] as usize) < a.len() {
+                    new[i] = a[mask[i] as usize];
+                } else if (mask[i] as usize - a.len()) < b.len() {
+                    new[i] = b[mask[i] as usize - a.len()];
+                } // else leave as 0.
             }
+            assign(Value::vector(new, ctrl_ty)?)
         }
         Opcode::Swizzle => {
             let x = Value::into_array(&arg(0)?)?;