diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index daf13bfc..f26babef 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -130,6 +130,32 @@ jobs:
             castxml-epic: 1
             cppstd: "-std=c++11"
 
+          # UBUNTU ARM
+          - os: ubuntu-22.04-arm
+            arch: aarch64
+            compiler: clang++
+            clang-version: 15
+            python-version: "3.13"
+            castxml-epic: 0
+            cppstd: "-std=c++17"
+
+          - os: ubuntu-24.04-arm
+            arch: aarch64
+            compiler: clang++
+            clang-version: 16
+            python-version: "3.13"
+            castxml-epic: 0
+            cppstd: "-std=c++17"
+
+          # UBUNTU 24.04 - CASTXML EPIC 1
+          - os: ubuntu-24.04-arm
+            arch: aarch64
+            compiler: clang++
+            clang-version: 16
+            python-version: "3.13"
+            castxml-epic: 1
+            cppstd: "-std=c++11"
+
           # MACOS
           - os: macos-13
             compiler: clang++
@@ -181,6 +207,21 @@ jobs:
           tar -xzf ~/castxml-ubuntu-22.04-x86_64.tar.gz -C ~/
           chmod +x ~/castxml/bin/castxml
 
+      # ─── Setup CastXML for Linux aarch64 ──────────────────────────────
+      - name: Setup CastXML for Linux aarch64 (Ubuntu 24.04)
+        if: matrix.os == 'ubuntu-24.04-arm' && matrix.arch == 'aarch64'
+        run: |
+          wget -q -O ~/castxml-ubuntu-24.04-arm-aarch64.tar.gz https://github.com/CastXML/CastXMLSuperbuild/releases/download/v0.6.11.post2/castxml-ubuntu-24.04-arm-aarch64.tar.gz
+          tar -xzf ~/castxml-ubuntu-24.04-arm-aarch64.tar.gz -C ~/
+          chmod +x ~/castxml/bin/castxml
+
+      - name: Setup CastXML for Linux aarch64 (Ubuntu 22.04)
+        if: matrix.os == 'ubuntu-22.04-arm' && matrix.arch == 'aarch64'
+        run: |
+          wget -q -O ~/castxml-ubuntu-22.04-arm-aarch64.tar.gz https://github.com/CastXML/CastXMLSuperbuild/releases/download/v0.6.11.post2/castxml-ubuntu-22.04-arm-aarch64.tar.gz
+          tar -xzf ~/castxml-ubuntu-22.04-arm-aarch64.tar.gz -C ~/
+          chmod +x ~/castxml/bin/castxml
+
       # ─── Setup CastXML for MacOS ──────────────────────────────
       - name: Setup CastXML for macOS (arm64)
         if: matrix.os == 'macos-15'
diff --git a/src/pygccxml/parser/project_reader.py b/src/pygccxml/parser/project_reader.py
index b37d8665..a4eaace1 100644
--- a/src/pygccxml/parser/project_reader.py
+++ b/src/pygccxml/parser/project_reader.py
@@ -353,7 +353,12 @@ def __parse_all_at_once(self, files):
                 header_content.append(
                     '#include "%s" %s' %
                     (header, os.linesep))
-        return self.read_string(''.join(header_content))
+        declarations = self.read_string(''.join(header_content))
+        declarations = self._join_top_namespaces(declarations, [])
+        for ns in declarations:
+            if isinstance(ns, pygccxml.declarations.namespace_t):
+                declarations_joiner.join_declarations(ns)
+        return declarations
 
     def read_string(self, content):
         """Parse a string containing C/C++ source code.
@@ -420,15 +425,24 @@ def read_xml(self, file_configuration):
     def _join_top_namespaces(main_ns_list, other_ns_list):
         answer = main_ns_list[:]
         for other_ns in other_ns_list:
-            main_ns = pygccxml.declarations.find_declaration(
+            same_name_namespaces = pygccxml.declarations.find_all_declarations(
                 answer,
                 decl_type=pygccxml.declarations.namespace_t,
-                name=other_ns._name,
-                recursive=False)
-            if main_ns:
-                main_ns.take_parenting(other_ns)
-            else:
+                name=other_ns.name,
+                parent=None,  # top-level only
+                recursive=False
+            )
+            if len(same_name_namespaces) == 0:
                 answer.append(other_ns)
+            elif len(same_name_namespaces) == 1:
+                same_name_namespaces[0].take_parenting(other_ns)
+            else:
+                primary_ns = same_name_namespaces[0]
+                for extra_ns in same_name_namespaces[1:]:
+                    primary_ns.take_parenting(extra_ns)
+                    answer.remove(extra_ns)
+                # then unify the new other_ns
+                primary_ns.take_parenting(other_ns)
         return answer
 
     @staticmethod