diff --git a/apps/regression/graph_controller.cpp b/apps/regression/graph_controller.cpp
index 93b5c5867..ebdebbb46 100644
--- a/apps/regression/graph_controller.cpp
+++ b/apps/regression/graph_controller.cpp
@@ -351,7 +351,7 @@ uint32_t GraphController::modelVersion() {
   return m_store->storeChecksum();
 }
 
-uint32_t GraphController::modelVersionAtIndex(size_t i) {
+uint32_t GraphController::modelVersionAtIndex(int i) {
   assert(i < numberOfMemoizedVersions());
   return *(m_store->seriesChecksum() + i);
 }
diff --git a/apps/regression/graph_controller.h b/apps/regression/graph_controller.h
index 30e722552..d81680c18 100644
--- a/apps/regression/graph_controller.h
+++ b/apps/regression/graph_controller.h
@@ -43,7 +43,7 @@ private:
   // InteractiveCurveViewController
   void initCursorParameters() override;
   uint32_t modelVersion() override;
-  uint32_t modelVersionAtIndex(size_t i) override;
+  uint32_t modelVersionAtIndex(int i) override;
   uint32_t rangeVersion() override;
   size_t numberOfMemoizedVersions() const override { return Store::k_numberOfSeries; }
   int selectedCurveIndex() const override { return *m_selectedSeriesIndex; }
diff --git a/apps/shared/function_graph_controller.cpp b/apps/shared/function_graph_controller.cpp
index f851f65ef..e1922ef6b 100644
--- a/apps/shared/function_graph_controller.cpp
+++ b/apps/shared/function_graph_controller.cpp
@@ -183,7 +183,7 @@ uint32_t FunctionGraphController::modelVersion() {
   return functionStore()->storeChecksum();
 }
 
-uint32_t FunctionGraphController::modelVersionAtIndex(size_t i) {
+uint32_t FunctionGraphController::modelVersionAtIndex(int i) {
   return functionStore()->storeChecksumAtIndex(i);
 }
 
diff --git a/apps/shared/function_graph_controller.h b/apps/shared/function_graph_controller.h
index fcb15ae57..9e7297efe 100644
--- a/apps/shared/function_graph_controller.h
+++ b/apps/shared/function_graph_controller.h
@@ -50,7 +50,7 @@ private:
   // InteractiveCurveViewController
   bool moveCursorVertically(int direction) override;
   uint32_t modelVersion() override;
-  uint32_t modelVersionAtIndex(size_t i) override;
+  uint32_t modelVersionAtIndex(int i) override;
   uint32_t rangeVersion() override;
   size_t numberOfMemoizedVersions() const override { return sNumberOfMemoizedModelVersions; }
 
diff --git a/apps/shared/function_store.cpp b/apps/shared/function_store.cpp
index 7a05715a2..4ef45d956 100644
--- a/apps/shared/function_store.cpp
+++ b/apps/shared/function_store.cpp
@@ -6,7 +6,7 @@ uint32_t FunctionStore::storeChecksum() {
   return Ion::Storage::sharedStorage()->checksum();
 }
 
-uint32_t FunctionStore::storeChecksumAtIndex(size_t i) {
+uint32_t FunctionStore::storeChecksumAtIndex(int i) {
   if (numberOfActiveFunctions() <= i) {
     return 0;
   }
diff --git a/apps/shared/function_store.h b/apps/shared/function_store.h
index 03e57ef58..0233a37dd 100644
--- a/apps/shared/function_store.h
+++ b/apps/shared/function_store.h
@@ -13,7 +13,7 @@ class FunctionStore : public ExpressionModelStore {
 public:
   FunctionStore() : ExpressionModelStore() {}
   uint32_t storeChecksum();
-  uint32_t storeChecksumAtIndex(size_t i);
+  uint32_t storeChecksumAtIndex(int i);
   int numberOfActiveFunctions() const {
     return numberOfModelsSatisfyingTest(&isFunctionActive, nullptr);
   }
diff --git a/apps/shared/interactive_curve_view_controller.h b/apps/shared/interactive_curve_view_controller.h
index 9ef048f18..c732ff524 100644
--- a/apps/shared/interactive_curve_view_controller.h
+++ b/apps/shared/interactive_curve_view_controller.h
@@ -41,7 +41,7 @@ protected:
   virtual void initCursorParameters() = 0;
   virtual bool moveCursorVertically(int direction) = 0;
   virtual uint32_t modelVersion() = 0;
-  virtual uint32_t modelVersionAtIndex(size_t i) = 0;
+  virtual uint32_t modelVersionAtIndex(int i) = 0;
   virtual uint32_t rangeVersion() = 0;
   bool isCursorVisible();