diff --git a/src/rp2_common/hardware_irq/irq.c b/src/rp2_common/hardware_irq/irq.c
index 2705e03..211f6d0 100644
--- a/src/rp2_common/hardware_irq/irq.c
+++ b/src/rp2_common/hardware_irq/irq.c
@@ -159,19 +159,18 @@ static inline void *resolve_branch(uint16_t *inst) {
 // GCC produces horrible code for subtraction of pointers here, and it was bugging me
 static inline int8_t slot_diff(struct irq_handler_chain_slot *to, struct irq_handler_chain_slot *from) {
     static_assert(sizeof(struct irq_handler_chain_slot) == 12, "");
-    int32_t result;
+    int32_t result = 0xaaaa;
     // return (to - from);
     // note this implementation has limited range, but is fine for plenty more than -128->127 result
     asm (".syntax unified\n"
          "subs %1, %2\n"
          "adcs %1, %1\n" // * 2 (and + 1 if negative for rounding)
-         "ldr  %0, =0xaaaa\n"
          "muls %0, %1\n"
          "lsrs %0, 20\n"
-        : "=l" (result), "+l" (to)
-        : "l" (from)
-        :
-        );
+         : "+l" (result), "+l" (to)
+         : "l" (from)
+         :
+         );
     return (int8_t)result;
 }