diff --git a/src/core/common_code/common_code.h b/src/core/common_code/common_code.h
index 6c6d034..d089f2e 100644
--- a/src/core/common_code/common_code.h
+++ b/src/core/common_code/common_code.h
@@ -102,7 +102,7 @@ public:
     // ------------------------------------------------------------------------------------- //
 
     /// Get the original u64 code.
-    [[nodiscard]] uint64_t unwrap() const;
+    [[nodiscard]] constexpr uint64_t unwrap() const;
 
     /// Convert CommonCode to RawCode.
     [[nodiscard]] RawCode to_raw_code() const;
diff --git a/src/core/common_code/internal/common_code.inl b/src/core/common_code/internal/common_code.inl
index 3b284a9..575bdb2 100644
--- a/src/core/common_code/internal/common_code.inl
+++ b/src/core/common_code/internal/common_code.inl
@@ -41,7 +41,7 @@ inline std::ostream& operator<<(std::ostream &out, const CommonCode self) {
 
 // ----------------------------------------------------------------------------------------- //
 
-inline uint64_t CommonCode::unwrap() const {
+constexpr uint64_t CommonCode::unwrap() const {
     return code_;
 }
 
diff --git a/src/core/group/group.h b/src/core/group/group.h
index a7f8b27..b60661c 100644
--- a/src/core/group/group.h
+++ b/src/core/group/group.h
@@ -125,7 +125,7 @@ public:
     static constexpr GroupUnion from_raw_code(codec::RawCode raw_code);
 
     /// Create GroupUnion from ShortCode.
-    static constexpr GroupUnion from_short_code(codec::ShortCode short_code);
+    static GroupUnion from_short_code(codec::ShortCode short_code);
 
     /// Create GroupUnion from CommonCode.
     static constexpr GroupUnion from_common_code(codec::CommonCode common_code);
diff --git a/src/core/group/internal/group_union.inl b/src/core/group/internal/group_union.inl
index 68d7f3f..72064eb 100644
--- a/src/core/group/internal/group_union.inl
+++ b/src/core/group/internal/group_union.inl
@@ -43,7 +43,7 @@ constexpr std::optional<GroupUnion> GroupUnion::create(const uint_fast8_t type_i
 
 #ifndef KLSK_NDEBUG
 inline std::ostream& operator<<(std::ostream &out, GroupUnion self) {
-    out << self.type_id_;
+    out << static_cast<int>(self.type_id_);
     return out;
 }
 #endif
@@ -58,7 +58,7 @@ constexpr GroupUnion GroupUnion::from_raw_code(const codec::RawCode raw_code) {
     return unsafe_create(type_id(raw_code));
 }
 
-constexpr GroupUnion GroupUnion::from_short_code(const codec::ShortCode short_code) {
+inline GroupUnion GroupUnion::from_short_code(const codec::ShortCode short_code) {
     return from_common_code(short_code.to_common_code());
 }
 
diff --git a/src/core/raw_code/internal/raw_code.inl b/src/core/raw_code/internal/raw_code.inl
index 43e70d3..7b13e65 100644
--- a/src/core/raw_code/internal/raw_code.inl
+++ b/src/core/raw_code/internal/raw_code.inl
@@ -27,7 +27,7 @@ inline RawCode::operator uint64_t() const {
     return code_;
 }
 
-inline uint64_t RawCode::unwrap() const {
+constexpr uint64_t RawCode::unwrap() const {
     return code_;
 }
 
diff --git a/src/core/raw_code/raw_code.h b/src/core/raw_code/raw_code.h
index ff5f8e9..7f5cd7b 100644
--- a/src/core/raw_code/raw_code.h
+++ b/src/core/raw_code/raw_code.h
@@ -101,7 +101,7 @@ public:
     // ------------------------------------------------------------------------------------- //
 
     /// Get the original u64 code.
-    [[nodiscard]] uint64_t unwrap() const;
+    [[nodiscard]] constexpr uint64_t unwrap() const;
 
     /// Convert RawCode to CommonCode.
     [[nodiscard]] CommonCode to_common_code() const;