diff --git a/slothy/core/dataflow.py b/slothy/core/dataflow.py
index 956f82aa..b7086f6c 100644
--- a/slothy/core/dataflow.py
+++ b/slothy/core/dataflow.py
@@ -779,7 +779,7 @@ def find_all_predecessors_input_registers(self, consumer, register_name):
         """ recursively finds the set of input registers registers that a certain value depends on."""
         # ignore the stack pointer
         if register_name == "sp":
-            return set()
+            return set(["sp"])
 
         producer = consumer.reg_state[register_name].src
         # if this is a virtual input instruction this is an actual input