diff --git a/cranelift/filetests/filetests/interpreter/fibonacci.clif b/cranelift/filetests/filetests/interpreter/fibonacci.clif
index 70515c4b20..bdce284f36 100644
--- a/cranelift/filetests/filetests/interpreter/fibonacci.clif
+++ b/cranelift/filetests/filetests/interpreter/fibonacci.clif
@@ -10,12 +10,12 @@ block0(v0: i32):
 
 block1(v4: i32, v5:i32):
     v6 = iconst.i32 1
-    v7 = irsub_imm v4, 2
+    v7 = iadd_imm v4, -2
     fallthrough block2(v7, v5, v6)
 
 block2(v10: i32, v11: i32, v12: i32): ; params: n, fib(n-1), fib(n-2)
     v13 = iadd v11, v12
-    v14 = irsub_imm v10, 1
+    v14 = iadd_imm v10, -1
     v15 = icmp_imm eq v14, 0
     brnz v15, block3(v13)
     jump block2(v14, v13, v11)
@@ -43,9 +43,9 @@ block0(v0: i32):
     fallthrough block1(v0)
 
 block1(v10: i32):
-    v11 = irsub_imm v10, 1
+    v11 = iadd_imm v10, -1
     v12 = call fn0(v11)
-    v13 = irsub_imm v10, 2
+    v13 = iadd_imm v10, -2
     v14 = call fn0(v13)
     v15 = iadd v12, v14
     return v15
diff --git a/cranelift/interpreter/src/interpreter.rs b/cranelift/interpreter/src/interpreter.rs
index 3dbbe1d69d..2a13a0c4ce 100644
--- a/cranelift/interpreter/src/interpreter.rs
+++ b/cranelift/interpreter/src/interpreter.rs
@@ -163,7 +163,7 @@ impl Interpreter {
                 let arg = frame.get(&arg);
                 let result = match opcode {
                     IaddImm => binary_op!(Add::add[arg, imm]; [I8, I16, I32, I64, F32, F64]; inst),
-                    IrsubImm => binary_op!(Sub::sub[arg, imm]; [I8, I16, I32, I64, F32, F64]; inst),
+                    IrsubImm => binary_op!(Sub::sub[imm, arg]; [I8, I16, I32, I64, F32, F64]; inst),
                     _ => unimplemented!("interpreter does not support opcode yet: {}", opcode),
                 }?;
                 frame.set(first_result(frame.function, inst), result);
@@ -349,9 +349,9 @@ mod tests {
     fn sanity() {
         let code = "function %test() -> b1 {
         block0:
-            v0 = iconst.i32 40
-            v1 = iadd_imm v0, 3
-            v2 = irsub_imm v1, 1
+            v0 = iconst.i32 1
+            v1 = iadd_imm v0, 1
+            v2 = irsub_imm v1, 44  ; 44 - 2 == 42 (see irsub_imm's semantics)
             v3 = icmp_imm eq v2, 42
             return v3
         }";