diff --git a/CMakeLists.txt b/CMakeLists.txt
index f4e9b02d5..094f19aa9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,10 +1,24 @@
 cmake_minimum_required(VERSION 3.15)
-project(c3c)
+
+# Grab the version
+file(READ "src/version.h" ver)
+if (NOT ${ver} MATCHES "COMPILER_VERSION \"([0-9]+.[0-9]+.[0-9]+)\"")
+    message(FATAL_ERROR "Compiler version could not be parsed from version.h")
+endif()
+
+# Set the project and version
+project(c3c VERSION ${CMAKE_MATCH_1})
+message("C3C version: ${CMAKE_PROJECT_VERSION}")
+
+# Enable fetching (for Windows)
 include(FetchContent)
 include(FeatureSummary)
 
+
 set(CMAKE_FIND_PACKAGE_SORT_ORDER NATURAL)
 set(CMAKE_FIND_PACKAGE_SORT_DIRECTION DEC)
+
+# We use C11 and C++17
 set(CMAKE_C_STANDARD 11)
 set(CMAKE_CXX_STANDARD 17)
 
diff --git a/src/compiler/sema_expr.c b/src/compiler/sema_expr.c
index c6ad586a2..b4b2287de 100644
--- a/src/compiler/sema_expr.c
+++ b/src/compiler/sema_expr.c
@@ -1237,17 +1237,25 @@ static inline bool sema_call_check_contract_param_match(SemaContext *context, De
 		SEMA_ERROR(expr, "You may not pass null to a '&' parameter.");
 		return false;
 	}
+	if (expr->expr_kind == EXPR_UNARY && expr->unary_expr.expr->expr_kind == EXPR_IDENTIFIER)
+	{
+		if (expr->unary_expr.expr->identifier_expr.decl->var.kind == VARDECL_CONST && param->var.out_param)
+		{
+			SEMA_ERROR(expr, "A const parameter may not be passed into a function or macro as an 'out' argument.");
+			return false;
+		}
+	}
 	if (expr->expr_kind != EXPR_IDENTIFIER) return true;
 	Decl *ident = expr->identifier_expr.decl;
 	if (ident->decl_kind != DECL_VAR) return true;
 	if (ident->var.out_param && param->var.in_param)
 	{
-		SEMA_ERROR(expr, "It's not allowed to pass an 'out' parameter into a function or macro as an 'in' argument.");
+		SEMA_ERROR(expr, "An 'out' parameter may not be passed into a function or macro as an 'in' argument.");
 		return false;
 	}
 	if (ident->var.in_param && param->var.out_param)
 	{
-		SEMA_ERROR(expr, "It's not allowed to pass an 'in' parameter into a function or macro as an 'out' argument.");
+		SEMA_ERROR(expr, "An 'in' parameter may not be passed into a function or macro as an 'out' argument.");
 		return false;
 	}
 	return true;
diff --git a/src/version.h b/src/version.h
index da6ec54c4..eee4ac948 100644
--- a/src/version.h
+++ b/src/version.h
@@ -1 +1 @@
-#define COMPILER_VERSION "0.4.100"
\ No newline at end of file
+#define COMPILER_VERSION "0.4.101"
\ No newline at end of file
diff --git a/test/test_suite/contracts/constant_out.c3 b/test/test_suite/contracts/constant_out.c3
new file mode 100644
index 000000000..9f98a7081
--- /dev/null
+++ b/test/test_suite/contracts/constant_out.c3
@@ -0,0 +1,36 @@
+module test;
+
+
+struct Abc
+{
+	int a;
+}
+
+fn void Abc.update(Abc* a, int ab)
+{
+	a.a = ab;
+}
+
+/**
+ * @param [out] a
+ **/
+fn void Abc.update_fail(Abc* a, int ab)
+{
+	a.a = ab;
+}
+
+const Abc X = { 2 };
+
+
+fn int main()
+{
+	const Abc Y = { 3 };
+	int* z = &X.a;
+	*z = 31;
+	X.update(1);
+	X.update_fail(2); // #error: const parameter may not
+	X.a = 32; // #error: cannot assign to a constant
+	Y.a = 34; // #error: cannot assign to a constant
+	return 0;
+}
+
diff --git a/test/test_suite/contracts/in_out.c3 b/test/test_suite/contracts/in_out.c3
index 359d4949a..97ca78f7a 100644
--- a/test/test_suite/contracts/in_out.c3
+++ b/test/test_suite/contracts/in_out.c3
@@ -12,7 +12,7 @@ fn void bar(Foo* f)
  **/
 fn void foo(Foo* f)
 {
-  bar(f); // #error: It's not allowed to pass an 'in'
+  bar(f); // #error: macro as an 'out' argument
 }
 
 /**
@@ -27,5 +27,5 @@ fn void foo2(Foo* f)
  **/
 fn void baz(Foo *f)
 {
-	foo2(f); // #error: It's not allowed to pass an 'out'
+	foo2(f); // #error: may not be passed into a function
 }
\ No newline at end of file