diff --git a/src/interpreter/instructions/call.rs b/src/interpreter/instructions/call.rs
index d58368c..f6375c4 100644
--- a/src/interpreter/instructions/call.rs
+++ b/src/interpreter/instructions/call.rs
@@ -6,7 +6,7 @@ use crate::interpreter::wasm::{
 executable_instruction!(
     call(function_index: usize, instruction_name: String) -> _ {
         move |runtime| -> _ {
-            let instance = runtime.wasm_instance;
+            let instance = &mut runtime.wasm_instance;
             let index = FunctionIndex::new(function_index);
 
             match instance.local_or_import(index) {
diff --git a/src/interpreter/instructions/call_export.rs b/src/interpreter/instructions/call_export.rs
index a1a4340..62e360a 100644
--- a/src/interpreter/instructions/call_export.rs
+++ b/src/interpreter/instructions/call_export.rs
@@ -3,7 +3,7 @@ use crate::interpreter::wasm::values::InterfaceType;
 executable_instruction!(
     call_export(export_name: String, instruction_name: String) -> _ {
         move |runtime| -> _ {
-            let instance = runtime.wasm_instance;
+            let instance = &mut runtime.wasm_instance;
 
             match instance.export(&export_name) {
                 Some(export) => {
diff --git a/src/interpreter/instructions/mod.rs b/src/interpreter/instructions/mod.rs
index 183e0dc..d84d2b4 100644
--- a/src/interpreter/instructions/mod.rs
+++ b/src/interpreter/instructions/mod.rs
@@ -175,7 +175,7 @@ pub(crate) mod tests {
         }
 
         fn local_or_import<I: wasm::structures::TypedIndex + wasm::structures::LocalImportIndex>(
-            &self,
+            &mut self,
             index: I,
         ) -> Option<&LocalImport> {
             self.locals_or_imports.get(&index.index())
diff --git a/src/interpreter/instructions/write_utf8.rs b/src/interpreter/instructions/write_utf8.rs
index b0738f3..a1e2150 100644
--- a/src/interpreter/instructions/write_utf8.rs
+++ b/src/interpreter/instructions/write_utf8.rs
@@ -4,7 +4,7 @@ use std::convert::TryInto;
 executable_instruction!(
     write_utf8(allocator_name: String, instruction_name: String) -> _ {
         move |runtime| -> _ {
-            let instance = runtime.wasm_instance;
+            let instance = &mut runtime.wasm_instance;
 
             match instance.export(&allocator_name) {
                 Some(allocator) => {
@@ -17,7 +17,7 @@ executable_instruction!(
                             ))
                         }
 
-                    match runtime.wasm_instance.memory(0) {
+                    match instance.memory(0) {
                         Some(memory) => match runtime.stack.pop1() {
                             Some(string) => {
                                 let memory_view = memory.view();
diff --git a/src/interpreter/mod.rs b/src/interpreter/mod.rs
index 1b133a7..551311a 100644
--- a/src/interpreter/mod.rs
+++ b/src/interpreter/mod.rs
@@ -18,7 +18,7 @@ where
 {
     invocation_inputs: &'invocation [InterfaceValue],
     stack: Stack<InterfaceValue>,
-    wasm_instance: &'instance Instance,
+    wasm_instance: &'instance mut Instance,
     _phantom: PhantomData<(Export, LocalImport, Memory, MemoryView)>,
 }
 
@@ -58,7 +58,7 @@ where
     pub fn run(
         &self,
         invocation_inputs: &[InterfaceValue],
-        wasm_instance: &Instance,
+        wasm_instance: &mut Instance,
     ) -> Result<Stack<InterfaceValue>, String> {
         let mut runtime = Runtime {
             invocation_inputs,
diff --git a/src/interpreter/wasm/structures.rs b/src/interpreter/wasm/structures.rs
index a38511c..7ec386f 100644
--- a/src/interpreter/wasm/structures.rs
+++ b/src/interpreter/wasm/structures.rs
@@ -70,7 +70,7 @@ where
     MV: MemoryView,
 {
     fn export(&self, export_name: &str) -> Option<&E>;
-    fn local_or_import<I: TypedIndex + LocalImportIndex>(&self, index: I) -> Option<&LI>;
+    fn local_or_import<I: TypedIndex + LocalImportIndex>(&mut self, index: I) -> Option<&LI>;
     fn memory(&self, index: usize) -> Option<&M>;
 }
 
@@ -151,7 +151,7 @@ where
         None
     }
 
-    fn local_or_import<I: TypedIndex + LocalImportIndex>(&self, _index: I) -> Option<&LI> {
+    fn local_or_import<I: TypedIndex + LocalImportIndex>(&mut self, _index: I) -> Option<&LI> {
         None
     }
 }
diff --git a/src/macros.rs b/src/macros.rs
index aee8178..a0b9994 100644
--- a/src/macros.rs
+++ b/src/macros.rs
@@ -68,8 +68,8 @@ macro_rules! test_executable_instruction {
                 (&vec![$($instructions),*]).try_into().unwrap();
 
             let invocation_inputs = vec![$($invocation_inputs),*];
-            let instance = $instance;
-            let run = interpreter.run(&invocation_inputs, &instance);
+            let mut instance = $instance;
+            let run = interpreter.run(&invocation_inputs, &mut instance);
 
             assert!(run.is_ok());
 
@@ -102,8 +102,8 @@ macro_rules! test_executable_instruction {
                 (&vec![$($instructions),*]).try_into().unwrap();
 
             let invocation_inputs = vec![$($invocation_inputs),*];
-            let instance = $instance;
-            let run = interpreter.run(&invocation_inputs, &instance);
+            let mut instance = $instance;
+            let run = interpreter.run(&invocation_inputs, &mut instance);
 
             assert!(run.is_err());