diff --git a/libcomps-c99.patch b/libcomps-c99.patch
new file mode 100644
index 0000000..7dc7933
--- /dev/null
+++ b/libcomps-c99.patch
@@ -0,0 +1,40 @@
+commit a71bce7e62990550a57688e51b14eb82d6de196b
+Author: Aleš Matěj <amatej@redhat.com>
+Date:   Tue Jan 2 08:32:55 2024 +0100
+
+    Fix build: use correct variable for category and env
+    
+    Fixes:
+    - error: assignment to ‘COMPS_DocGroup *’ from incompatible pointer type ‘COMPS_DocCategory *’
+    - error: assignment to ‘COMPS_DocGroup *’ from incompatible pointer type ‘COMPS_DocEnv *’
+    
+    For: https://fedoraproject.org/wiki/Changes/PortingToModernC
+    (https://fedoraproject.org/wiki/Toolchain/PortingToModernC)
+    (https://gitlab.com/fweimer-rh/fedora-modernc-logs/-/blob/main/logs/l/libcomps.log)
+
+diff --git a/libcomps/tests/check_parse.c b/libcomps/tests/check_parse.c
+index e5935e129e43e4e7..689cb98da3a631b0 100644
+--- a/libcomps/tests/check_parse.c
++++ b/libcomps/tests/check_parse.c
+@@ -585,8 +585,8 @@ START_TEST(test_arch)
+     list = comps_doc_categories(doc2);
+     ck_assert(list->len == 2);
+     for (it = list->first, x=0; it != NULL; it = it->next, x++) {
+-        g = (COMPS_DocCategory*)it->comps_obj;
+-        str = (COMPS_Str*)comps_doccategory_get_id(g);
++        c = (COMPS_DocCategory*)it->comps_obj;
++        str = (COMPS_Str*)comps_doccategory_get_id(c);
+         ck_assert_msg(strcmp(str->val, cats[0][x]) == 0, "%s != %s",
+                       str->val, cats[0][x]);
+         COMPS_OBJECT_DESTROY(str);
+@@ -605,8 +605,8 @@ START_TEST(test_arch)
+     list = comps_doc_environments(doc2);
+     ck_assert(list->len == 2);
+     for (it = list->first, x=0; it != NULL; it = it->next, x++) {
+-        g = (COMPS_DocEnv*)it->comps_obj;
+-        str = (COMPS_Str*)comps_docenv_get_id(g);
++        e = (COMPS_DocEnv*)it->comps_obj;
++        str = (COMPS_Str*)comps_docenv_get_id(e);
+         ck_assert_msg(strcmp(str->val, envs[0][x]) == 0, "%s != %s",
+                       str->val, envs[0][x]);
+         COMPS_OBJECT_DESTROY(str);
diff --git a/libcomps.spec b/libcomps.spec
index b10bb09..5d80aa0 100644
--- a/libcomps.spec
+++ b/libcomps.spec
@@ -2,7 +2,7 @@
 
 Name:           libcomps
 Version:        0.1.20
-Release:        2%{?dist}
+Release:        3%{?dist}
 Summary:        Comps XML file manipulation library
 
 License:        GPL-2.0-or-later
@@ -12,6 +12,7 @@ Source0:        %{url}/archive/%{version}/%{name}-%{version}.tar.gz
 # Fix build with libxml2 2.12.0
 # https://github.com/rpm-software-management/libcomps/pull/109
 Patch0:         fix-build-libxml2-2.12.0.patch
+Patch1: libcomps-c99.patch
 
 BuildRequires:  gcc-c++
 BuildRequires:  cmake
@@ -120,6 +121,9 @@ popd
 %{python3_sitearch}/%{name}-%{version}-py%{python3_version}.egg-info
 
 %changelog
+* Wed Jan 03 2024 Florian Weimer <fweimer@redhat.com> - 0.1.20-3
+- Backport upstream patch to fix C compatibility issue
+
 * Wed Dec 13 2023 Yaakov Selkowitz <yselkowi@redhat.com> - 0.1.20-2
 - Fix build with libxml2-2.12.0