diff --git a/src/compiler/sema_expr.c b/src/compiler/sema_expr.c
index cee8543a7..6363f531f 100644
--- a/src/compiler/sema_expr.c
+++ b/src/compiler/sema_expr.c
@@ -4034,7 +4034,7 @@ static inline bool sema_expr_analyse_struct_plain_initializer(SemaContext *conte
 		Decl *member = members[i];
 		if (member->decl_kind != DECL_VAR && !member->name)
 		{
-			int sub_element_count = decl_count_elements(members[i]);
+			int sub_element_count = decl_count_elements(member);
 			if (!sub_element_count)
 			{
 				vec_add(initializer->initializer_list, NULL);
@@ -4093,9 +4093,28 @@ static inline bool sema_expr_analyse_struct_plain_initializer(SemaContext *conte
 
 	if (expr_is_constant_eval(initializer, CONSTANT_EVAL_ANY))
 	{
+		bool is_union = type_flatten_distinct(initializer->type)->type_kind == TYPE_UNION;
+		assert(!is_union || vec_size(elements) == 1);
 		ConstInitializer *const_init = CALLOCS(ConstInitializer);
-		const_init->kind = CONST_INIT_STRUCT;
+		const_init->kind = is_union ? CONST_INIT_UNION : CONST_INIT_STRUCT;
 		const_init->type = type_flatten(initializer->type);
+		if (is_union)
+		{
+			Expr *expr = elements[0];
+			const_init->init_union.index = 0;
+			if (expr->expr_kind == EXPR_CONST && expr->const_expr.const_kind == CONST_LIST)
+			{
+				const_init->init_union.element = expr->const_expr.list;
+			}
+			else
+			{
+				ConstInitializer *element_init = MALLOCS(ConstInitializer);
+				sema_create_const_initializer_value(element_init, expr);
+				const_init->init_union.element = element_init;
+			}
+			expr_set_as_const_list(initializer, const_init);
+			return true;
+		}
 		ConstInitializer **inits = MALLOC(sizeof(ConstInitializer *) * vec_size(elements));
 		VECEACH(elements, i)
 		{
diff --git a/src/version.h b/src/version.h
index 5d8065056..9bd0e304f 100644
--- a/src/version.h
+++ b/src/version.h
@@ -1 +1 @@
-#define COMPILER_VERSION "0.2.11"
\ No newline at end of file
+#define COMPILER_VERSION "0.2.12"
\ No newline at end of file
diff --git a/test/test_suite/struct/nested_struct_union_init.c3t b/test/test_suite/struct/nested_struct_union_init.c3t
new file mode 100644
index 000000000..67ffafa58
--- /dev/null
+++ b/test/test_suite/struct/nested_struct_union_init.c3t
@@ -0,0 +1,116 @@
+// #target: macos-x64
+module foob;
+import libc;
+struct Matrix2x2
+{
+	union
+	{
+		float[4] m;
+		struct {
+			float m00, m01, m10, m11;
+		}
+	}
+}
+
+struct Matrix2x2_b
+{
+	union
+	{
+		struct {
+			float m00, m01, m10, m11;
+		}
+		float[4] m;
+	}
+}
+struct Matrix4x4 {
+    union {
+        struct {
+            float m00, m01, m02, m03;
+            float m10, m11, m12, m13;
+            float m20, m21, m22, m23;
+            float m30, m31, m32, m33;
+        }
+        float[16] m;
+    }
+}
+
+
+struct Matrix3x3 {
+    union {
+        struct {
+            float m00, m01, m02, m10, m11, m12, m20, m21, m22;
+        }
+        float[9] m;
+    }
+}
+fn void main()
+{
+	Matrix3x3 x = { 1, 2, 3, 4, 5, 6, 7,8 ,9};
+	Matrix2x2 m = { float[4] { 1, 2, 3, 4 } };
+	Matrix2x2_b m2 = { 1, 2, 3, 4 };
+	libc::printf("%f %f %f %f\n", x.m00, x.m[1], x.m10, x.m[3]);
+}
+
+/* #expect: foob.ll
+
+%Matrix2x2 = type { %anon.1 }
+%anon.1 = type { [4 x float] }
+%Matrix2x2_b = type { %anon.2 }
+%anon.2 = type { %anon.3 }
+%anon.3 = type { float, float, float, float }
+%Matrix3x3 = type { %anon }
+%anon = type { %anon.0 }
+%anon.0 = type { float, float, float, float, float, float, float, float, float }
+
+define void @foob.main() #0 {
+entry:
+  %x = alloca %Matrix3x3, align 4
+  %m = alloca %Matrix2x2, align 4
+  %m2 = alloca %Matrix2x2_b, align 4
+  %0 = getelementptr inbounds %Matrix3x3, %Matrix3x3* %x, i32 0, i32 0
+  %1 = bitcast %anon* %0 to %anon.0*
+  %2 = getelementptr inbounds %anon.0, %anon.0* %1, i32 0, i32 0
+  store float 1.000000e+00, float* %2, align 4
+  %3 = getelementptr inbounds %anon.0, %anon.0* %1, i32 0, i32 1
+  store float 2.000000e+00, float* %3, align 4
+  %4 = getelementptr inbounds %anon.0, %anon.0* %1, i32 0, i32 2
+  store float 3.000000e+00, float* %4, align 4
+  %5 = getelementptr inbounds %anon.0, %anon.0* %1, i32 0, i32 3
+  store float 4.000000e+00, float* %5, align 4
+  %6 = getelementptr inbounds %anon.0, %anon.0* %1, i32 0, i32 4
+  store float 5.000000e+00, float* %6, align 4
+  %7 = getelementptr inbounds %anon.0, %anon.0* %1, i32 0, i32 5
+  store float 6.000000e+00, float* %7, align 4
+  %8 = getelementptr inbounds %anon.0, %anon.0* %1, i32 0, i32 6
+  store float 7.000000e+00, float* %8, align 4
+  %9 = getelementptr inbounds %anon.0, %anon.0* %1, i32 0, i32 7
+  store float 8.000000e+00, float* %9, align 4
+  %10 = getelementptr inbounds %anon.0, %anon.0* %1, i32 0, i32 8
+  store float 9.000000e+00, float* %10, align 4
+  %11 = bitcast %Matrix2x2* %m to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 %11, i8* align 4 bitcast (%Matrix2x2* @.__const to i8*), i32 16, i1 false)
+  %12 = bitcast %Matrix2x2_b* %m2 to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 %12, i8* align 4 bitcast (%Matrix2x2_b* @.__const.8 to i8*), i32 16, i1 false)
+  %13 = getelementptr inbounds %Matrix3x3, %Matrix3x3* %x, i32 0, i32 0
+  %14 = bitcast %anon* %13 to %anon.0*
+  %15 = getelementptr inbounds %anon.0, %anon.0* %14, i32 0, i32 0
+  %16 = load float, float* %15, align 4
+  %fpfpext = fpext float %16 to double
+  %17 = getelementptr inbounds %Matrix3x3, %Matrix3x3* %x, i32 0, i32 0
+  %18 = bitcast %anon* %17 to [9 x float]*
+  %19 = getelementptr inbounds [9 x float], [9 x float]* %18, i64 0, i64 1
+  %20 = load float, float* %19, align 4
+  %fpfpext1 = fpext float %20 to double
+  %21 = getelementptr inbounds %Matrix3x3, %Matrix3x3* %x, i32 0, i32 0
+  %22 = bitcast %anon* %21 to %anon.0*
+  %23 = getelementptr inbounds %anon.0, %anon.0* %22, i32 0, i32 3
+  %24 = load float, float* %23, align 4
+  %fpfpext2 = fpext float %24 to double
+  %25 = getelementptr inbounds %Matrix3x3, %Matrix3x3* %x, i32 0, i32 0
+  %26 = bitcast %anon* %25 to [9 x float]*
+  %27 = getelementptr inbounds [9 x float], [9 x float]* %26, i64 0, i64 3
+  %28 = load float, float* %27, align 4
+  %fpfpext3 = fpext float %28 to double
+  %29 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([13 x i8], [13 x i8]* @.str, i32 0, i32 0), double %fpfpext, double %fpfpext1, double %fpfpext2, double %fpfpext3)
+  ret void
+}
diff --git a/test/test_suite2/struct/nested_struct_union_init.c3t b/test/test_suite2/struct/nested_struct_union_init.c3t
new file mode 100644
index 000000000..22637eb52
--- /dev/null
+++ b/test/test_suite2/struct/nested_struct_union_init.c3t
@@ -0,0 +1,110 @@
+// #target: macos-x64
+module foob;
+import libc;
+struct Matrix2x2
+{
+	union
+	{
+		float[4] m;
+		struct {
+			float m00, m01, m10, m11;
+		}
+	}
+}
+
+struct Matrix2x2_b
+{
+	union
+	{
+		struct {
+			float m00, m01, m10, m11;
+		}
+		float[4] m;
+	}
+}
+struct Matrix4x4 {
+    union {
+        struct {
+            float m00, m01, m02, m03;
+            float m10, m11, m12, m13;
+            float m20, m21, m22, m23;
+            float m30, m31, m32, m33;
+        }
+        float[16] m;
+    }
+}
+
+
+struct Matrix3x3 {
+    union {
+        struct {
+            float m00, m01, m02, m10, m11, m12, m20, m21, m22;
+        }
+        float[9] m;
+    }
+}
+fn void main()
+{
+	Matrix3x3 x = { 1, 2, 3, 4, 5, 6, 7,8 ,9};
+	Matrix2x2 m = { float[4] { 1, 2, 3, 4 } };
+	Matrix2x2_b m2 = { 1, 2, 3, 4 };
+	libc::printf("%f %f %f %f\n", x.m00, x.m[1], x.m10, x.m[3]);
+}
+
+/* #expect: foob.ll
+
+%Matrix2x2 = type { %anon.1 }
+%anon.1 = type { [4 x float] }
+%Matrix2x2_b = type { %anon.2 }
+%anon.2 = type { %anon.3 }
+%anon.3 = type { float, float, float, float }
+%Matrix3x3 = type { %anon }
+%anon = type { %anon.0 }
+%anon.0 = type { float, float, float, float, float, float, float, float, float }
+
+
+define void @foob.main() #0 {
+entry:
+  %x = alloca %Matrix3x3, align 4
+  %m = alloca %Matrix2x2, align 4
+  %m2 = alloca %Matrix2x2_b, align 4
+  %0 = getelementptr inbounds %Matrix3x3, ptr %x, i32 0, i32 0
+  %1 = getelementptr inbounds %anon.0, ptr %0, i32 0, i32 0
+  store float 1.000000e+00, ptr %1, align 4
+  %2 = getelementptr inbounds %anon.0, ptr %0, i32 0, i32 1
+  store float 2.000000e+00, ptr %2, align 4
+  %3 = getelementptr inbounds %anon.0, ptr %0, i32 0, i32 2
+  store float 3.000000e+00, ptr %3, align 4
+  %4 = getelementptr inbounds %anon.0, ptr %0, i32 0, i32 3
+  store float 4.000000e+00, ptr %4, align 4
+  %5 = getelementptr inbounds %anon.0, ptr %0, i32 0, i32 4
+  store float 5.000000e+00, ptr %5, align 4
+  %6 = getelementptr inbounds %anon.0, ptr %0, i32 0, i32 5
+  store float 6.000000e+00, ptr %6, align 4
+  %7 = getelementptr inbounds %anon.0, ptr %0, i32 0, i32 6
+  store float 7.000000e+00, ptr %7, align 4
+  %8 = getelementptr inbounds %anon.0, ptr %0, i32 0, i32 7
+  store float 8.000000e+00, ptr %8, align 4
+  %9 = getelementptr inbounds %anon.0, ptr %0, i32 0, i32 8
+  store float 9.000000e+00, ptr %9, align 4
+  call void @llvm.memcpy.p0.p0.i32(ptr align 4 %m, ptr align 4 @.__const, i32 16, i1 false)
+  call void @llvm.memcpy.p0.p0.i32(ptr align 4 %m2, ptr align 4 @.__const.8, i32 16, i1 false)
+  %10 = getelementptr inbounds %Matrix3x3, ptr %x, i32 0, i32 0
+  %11 = getelementptr inbounds %anon.0, ptr %10, i32 0, i32 0
+  %12 = load float, ptr %11, align 4
+  %fpfpext = fpext float %12 to double
+  %13 = getelementptr inbounds %Matrix3x3, ptr %x, i32 0, i32 0
+  %14 = getelementptr inbounds [9 x float], ptr %13, i64 0, i64 1
+  %15 = load float, ptr %14, align 4
+  %fpfpext1 = fpext float %15 to double
+  %16 = getelementptr inbounds %Matrix3x3, ptr %x, i32 0, i32 0
+  %17 = getelementptr inbounds %anon.0, ptr %16, i32 0, i32 3
+  %18 = load float, ptr %17, align 4
+  %fpfpext2 = fpext float %18 to double
+  %19 = getelementptr inbounds %Matrix3x3, ptr %x, i32 0, i32 0
+  %20 = getelementptr inbounds [9 x float], ptr %19, i64 0, i64 3
+  %21 = load float, ptr %20, align 4
+  %fpfpext3 = fpext float %21 to double
+  %22 = call i32 (ptr, ...) @printf(ptr @.str, double %fpfpext, double %fpfpext1, double %fpfpext2, double %fpfpext3)
+  ret void
+}