diff --git a/vala-register_plugin_type-c99.patch b/vala-register_plugin_type-c99.patch
new file mode 100644
index 0000000..b91ccf8
--- /dev/null
+++ b/vala-register_plugin_type-c99.patch
@@ -0,0 +1,66 @@
+commit a902d7eae96a3f1ab0cb64f268443b23ee8ab45a
+Author: Rico Tzschichholz <ricotz@ubuntu.com>
+Date:   Sat Mar 18 12:40:55 2023 +0100
+
+    codegen: Add declaration for register call of dynamic DBus interfaces
+    
+    The call was added without the required extern declaration
+    
+    Found by -Werror=implicit-function-declaration
+    
+    Fixes https://gitlab.gnome.org/GNOME/vala/issues/1422
+
+diff --git a/codegen/valaccodemethodmodule.vala b/codegen/valaccodemethodmodule.vala
+index 77ff73c3120bcafd..6edafac6a07e7cb4 100644
+--- a/codegen/valaccodemethodmodule.vala
++++ b/codegen/valaccodemethodmodule.vala
+@@ -291,6 +291,12 @@ public abstract class Vala.CCodeMethodModule : CCodeStructModule {
+ 			}
+ 		}
+ 
++		unowned Interface? iface = type_symbol as Interface;
++		bool is_dbus_interface = false;
++		if (iface != null) {
++			is_dbus_interface = GDBusModule.get_dbus_name (type_symbol) != null;
++		}
++
+ 		// Add function prototypes for required register-type-calls which are likely external
+ 		if (type_symbol.source_reference.file != cfile.file) {
+ 			// TODO Duplicated source with TypeRegisterFunction.init_from_type()
+@@ -298,22 +304,26 @@ public abstract class Vala.CCodeMethodModule : CCodeStructModule {
+ 			register_func.add_parameter (new CCodeParameter ("module", "GTypeModule *"));
+ 			register_func.is_declaration = true;
+ 			cfile.add_function_declaration (register_func);
++
++			// TODO Duplicated source with GDBusClientModule.generate_interface_declaration()
++			if (is_dbus_interface) {
++				var proxy_register_type = new CCodeFunction ("%sproxy_register_dynamic_type".printf (get_ccode_lower_case_prefix (iface)));
++				proxy_register_type.add_parameter (new CCodeParameter ("module", "GTypeModule*"));
++				proxy_register_type.modifiers |= CCodeModifiers.EXTERN;
++				cfile.add_function_declaration (proxy_register_type);
++				requires_vala_extern = true;
++			}
+ 		}
+ 
+ 		var register_call = new CCodeFunctionCall (new CCodeIdentifier ("%s_register_type".printf (get_ccode_lower_case_name (type_symbol, null))));
+ 		register_call.add_argument (new CCodeIdentifier (module_init_param_name));
+ 		ccode.add_expression (register_call);
+ 
+-		var iface = type_symbol as Interface;
+-		if (iface != null) {
+-			string? dbus_name = GDBusModule.get_dbus_name(type_symbol);
+-
+-			if (dbus_name != null) {
+-				string proxy_cname = get_ccode_lower_case_prefix (type_symbol) + "proxy";
+-				var register_proxy = new CCodeFunctionCall (new CCodeIdentifier ("%s_register_dynamic_type".printf (proxy_cname)));
+-				register_proxy.add_argument (new CCodeIdentifier (module_init_param_name));
+-				ccode.add_expression (register_proxy);
+-			}
++		if (is_dbus_interface) {
++			string proxy_cname = get_ccode_lower_case_prefix (type_symbol) + "proxy";
++			var register_proxy = new CCodeFunctionCall (new CCodeIdentifier ("%s_register_dynamic_type".printf (proxy_cname)));
++			register_proxy.add_argument (new CCodeIdentifier (module_init_param_name));
++			ccode.add_expression (register_proxy);
+ 		}
+ 	}
+ 
diff --git a/vala.spec b/vala.spec
index d7ea155..ee48393 100644
--- a/vala.spec
+++ b/vala.spec
@@ -3,13 +3,14 @@
 
 Name:           vala
 Version:        0.56.4
-Release:        1%{?dist}
+Release:        2%{?dist}
 Summary:        A modern programming language for GNOME
 
 # Most files are LGPLv2.1+, curses.vapi is 2-clause BSD
 License:        LGPL-2.1-or-later AND BSD-2-Clause
 URL:            https://wiki.gnome.org/Projects/Vala
 Source0:        https://download.gnome.org/sources/%{name}/0.56/%{name}-%{version}.tar.xz
+Patch0: vala-register_plugin_type-c99.patch
 
 BuildRequires:  bison
 BuildRequires:  flex
@@ -19,7 +20,7 @@ BuildRequires:  libxslt
 BuildRequires:  make
 BuildRequires:  pkgconfig(gobject-2.0)
 # only if Vala source files are patched
-#BuildRequires:  vala
+BuildRequires:  vala
 
 # for tests
 BuildRequires:  dbus-x11
@@ -194,6 +195,9 @@ export -n VALAFLAGS
 
 
 %changelog
+* Mon Mar 20 2023 Florian Weimer <fweimer@redhat.com> - 0.56.4-2
+- Apply upstream patch to fix C99 issue in generated code (#2179136)
+
 * Thu Mar 09 2023 David King <amigadave@amigadave.com> - 0.56.4-1
 - Update to 0.56.4