diff --git a/include/jstar/jstar.h b/include/jstar/jstar.h
index f74e5e00..68b40240 100644
--- a/include/jstar/jstar.h
+++ b/include/jstar/jstar.h
@@ -176,7 +176,11 @@ JSTAR_API void jsrPushTuple(JStarVM* vm, size_t size);
 JSTAR_API void jsrPushTable(JStarVM* vm);
 JSTAR_API void jsrPushValue(JStarVM* vm, int slot);
 JSTAR_API void* jsrPushUserdata(JStarVM* vm, size_t size, void (*finalize)(void*));
-JSTAR_API void jsrPushNative(JStarVM* vm, const char* module, const char* name, JStarNative nat,
+
+// Push a native function to the top of the stack.
+// Returns true on success, leaving the native function on top of the stack.
+// Retruns false if the module could not be found, leaving an exception on top of the stack.
+JSTAR_API bool jsrPushNative(JStarVM* vm, const char* module, const char* name, JStarNative nat,
                              uint8_t argc);
 
 #define jsrDup(vm) jsrPushValue(vm, -1)
@@ -334,14 +338,14 @@ JSTAR_API size_t jsrGetLength(JStarVM* vm, int slot);
 // INSTANCE API
 // -----------------------------------------------------------------------------
 
-// Set the field `name` of the value at `slot` with the value on top of the stack
-// The value is not popped
-// Returns true in case of success
-// Returns false otherwise leaving an exception on top of the stack
+// Set the field `name` of the value at `slot` with the value on top of the stack.
+// The value is not popped.
+// Returns true in case of success.
+// Returns false otherwise leaving an exception on top of the stack.
 JSTAR_API bool jsrSetField(JStarVM* vm, int slot, const char* name);
 
-// Get the field `name` of the value at `slot`
-// Returns true in case of success leaving the result on top of the stack
+// Get the field `name` of the value at `slot`.
+// Returns true in case of success leaving the result on top of the stack.
 // Returns false otherwise leaving an exception on top of the stack.
 JSTAR_API bool jsrGetField(JStarVM* vm, int slot, const char* name);
 
@@ -349,15 +353,18 @@ JSTAR_API bool jsrGetField(JStarVM* vm, int slot, const char* name);
 // MODULE API
 // -----------------------------------------------------------------------------
 
-// Set the global `name` of the module `module` with the value on top of the stack
-// The value is not popped
-// If calling inside a native "module" can be NULL, and the used module will be the current one
-JSTAR_API void jsrSetGlobal(JStarVM* vm, const char* module, const char* name);
+// Set the global `name` of the module `module` with the value on top of the stack.
+// The value is not popped.
+// If calling inside a native "module" can be NULL, and the used module will be the current one.
+// Returns true in case of success, false if the module could not be found, leaving an exception
+// on top of the stack.
+JSTAR_API bool jsrSetGlobal(JStarVM* vm, const char* module, const char* name);
 
-// Get the global `name` of the module `module`
-// Returns true in case of success leaving the result on the top of the stack
-// Returns false otherwise leaving an exception on top of the stack
-// If calling inside a native "module" can be NULL, and the used module will be the current one
+// Get the global `name` of the module `module`.
+// Returns true in case of success leaving the result on the top of the stack.
+// Returns false if the module could not be found or the name could not be found in the module,
+// leaving an exception on top of the stack.
+// If calling inside a native "module" can be NULL, and the used module will be the current one.
 JSTAR_API bool jsrGetGlobal(JStarVM* vm, const char* module, const char* name);
 
 // -----------------------------------------------------------------------------
diff --git a/src/jstar.c b/src/jstar.c
index 2c92fd21..b0885803 100644
--- a/src/jstar.c
+++ b/src/jstar.c
@@ -54,6 +54,19 @@ static Value apiStackSlot(const JStarVM* vm, int slot) {
     return vm->apiStack[slot];
 }
 
+static ObjModule* getModuleOrRaise(JStarVM* vm, const char* module) {
+    ObjModule* mod = module ? getModule(vm, copyString(vm, module, strlen(module))) : vm->module;
+    if(!mod) {
+        if(module)
+            jsrRaise(vm, "ImportException", "Module '%s' not found.", module);
+        else
+            jsrRaise(vm, "ImportException",
+                     "No current module loaded, pass an explicit module name.");
+        return NULL;
+    }
+    return mod;
+}
+
 void jsrPrintErrorCB(JStarVM* vm, JStarResult err, const char* file, int line, const char* error) {
     if(line >= 0) {
         fprintf(stderr, "File %s [line:%d]:\n", file, line);
@@ -510,11 +523,11 @@ void* jsrPushUserdata(JStarVM* vm, size_t size, void (*finalize)(void*)) {
     return (void*)udata->data;
 }
 
-void jsrPushNative(JStarVM* vm, const char* module, const char* name, JStarNative nat,
+bool jsrPushNative(JStarVM* vm, const char* module, const char* name, JStarNative nat,
                    uint8_t argc) {
     checkStack(vm);
-    ObjModule* mod = getModule(vm, copyString(vm, module, strlen(module)));
-    JSR_ASSERT(mod, "Cannot find module");
+    ObjModule* mod = getModuleOrRaise(vm, module);
+    if(!mod) return false;
 
     ObjString* nativeName = copyString(vm, name, strlen(name));
     push(vm, OBJ_VAL(nativeName));
@@ -524,6 +537,7 @@ void jsrPushNative(JStarVM* vm, const char* module, const char* name, JStarNativ
     pop(vm);
 
     push(vm, OBJ_VAL(native));
+    return true;
 }
 
 void jsrPop(JStarVM* vm) {
@@ -542,10 +556,11 @@ int jsrTop(const JStarVM* vm) {
     return apiStackIndex(vm, -1);
 }
 
-void jsrSetGlobal(JStarVM* vm, const char* module, const char* name) {
-    ObjModule* mod = module ? getModule(vm, copyString(vm, module, strlen(module))) : vm->module;
-    JSR_ASSERT(mod, "Module doesn't exist");
+bool jsrSetGlobal(JStarVM* vm, const char* module, const char* name) {
+    ObjModule* mod = getModuleOrRaise(vm, module);
+    if(!mod) return false;
     hashTablePut(&mod->globals, copyString(vm, name, strlen(name)), peek(vm));
+    return true;
 }
 
 bool jsrIter(JStarVM* vm, int iterable, int res, bool* err) {
@@ -661,8 +676,8 @@ bool jsrGetField(JStarVM* vm, int slot, const char* name) {
 }
 
 bool jsrGetGlobal(JStarVM* vm, const char* module, const char* name) {
-    ObjModule* mod = module ? getModule(vm, copyString(vm, module, strlen(module))) : vm->module;
-    JSR_ASSERT(mod, "Module doesn't exist");
+    ObjModule* mod = getModuleOrRaise(vm, module);
+    if(!mod) return false;
 
     Value res;
     ObjString* nameStr = copyString(vm, name, strlen(name));