diff --git a/SuperLU-c99.patch b/SuperLU-c99.patch
new file mode 100644
index 0000000..4f7cf33
--- /dev/null
+++ b/SuperLU-c99.patch
@@ -0,0 +1,291 @@
+Avoid implicit function declarations and implicit ints for improved
+compatibility with future compilers.
+
+Submitted upstream: <https://github.com/xiaoyeli/superlu/pull/76>
+
+diff --git a/EXAMPLE/cfgmr.c b/EXAMPLE/cfgmr.c
+index 0f25f58923aa0c7e..d8f523f9b67fa5ca 100644
+--- a/EXAMPLE/cfgmr.c
++++ b/EXAMPLE/cfgmr.c
+@@ -33,6 +33,8 @@ For information on ITSOL contact saad@cs.umn.edu
+ 
+ #define  epsmac  1.0e-16
+ 
++extern int ccopy_(int *, complex *, int *, complex *, int *);
++extern void caxpy_(int *, complex *, complex *, int *, complex *, int *);
+ extern void cdotc_(complex *, int *, complex [], int *, complex [], int *);
+ extern float scnrm2_(int *, complex [], int *);
+ 
+diff --git a/EXAMPLE/clinsolx.c b/EXAMPLE/clinsolx.c
+index bcf91124458cabbd..e4401b01b03e087f 100644
+--- a/EXAMPLE/clinsolx.c
++++ b/EXAMPLE/clinsolx.c
+@@ -18,6 +18,8 @@ at the top-level directory.
+  */
+ #include "slu_cdefs.h"
+ 
++#include <unistd.h>
++
+ int main(int argc, char *argv[])
+ {
+     char           equed[1];
+diff --git a/EXAMPLE/clinsolx1.c b/EXAMPLE/clinsolx1.c
+index 8c540d172194c9ad..8a4e8e5a2aa79ea9 100644
+--- a/EXAMPLE/clinsolx1.c
++++ b/EXAMPLE/clinsolx1.c
+@@ -20,6 +20,8 @@ at the top-level directory.
+  */
+ #include "slu_cdefs.h"
+ 
++#include <unistd.h>
++
+ int main(int argc, char *argv[])
+ {
+ /*
+diff --git a/EXAMPLE/clinsolx2.c b/EXAMPLE/clinsolx2.c
+index 7fd680456c2baf3e..038bb4a77e41b3c8 100644
+--- a/EXAMPLE/clinsolx2.c
++++ b/EXAMPLE/clinsolx2.c
+@@ -20,6 +20,8 @@ at the top-level directory.
+  */
+ #include "slu_cdefs.h"
+ 
++#include <unistd.h>
++
+ int main(int argc, char *argv[])
+ {
+ /*
+diff --git a/EXAMPLE/clinsolx3.c b/EXAMPLE/clinsolx3.c
+index 973eb2736b00fb4b..33a1ac2e164841b3 100644
+--- a/EXAMPLE/clinsolx3.c
++++ b/EXAMPLE/clinsolx3.c
+@@ -20,6 +20,8 @@ at the top-level directory.
+  */
+ #include "slu_cdefs.h"
+ 
++#include <unistd.h>
++
+ int main(int argc, char *argv[])
+ {
+ /*
+diff --git a/EXAMPLE/dfgmr.c b/EXAMPLE/dfgmr.c
+index e19f11968199b7d3..97a3250c884d5495 100644
+--- a/EXAMPLE/dfgmr.c
++++ b/EXAMPLE/dfgmr.c
+@@ -33,6 +33,8 @@ For information on ITSOL contact saad@cs.umn.edu
+ 
+ #define  epsmac  1.0e-16
+ 
++extern int dcopy_(int *, double *, int *, double *, int *);
++extern void daxpy_(int *, double *, double *, int *, double *, int *);
+ extern double ddot_(int *, double [], int *, double [], int *);
+ extern double dnrm2_(int *, double [], int *);
+ 
+diff --git a/EXAMPLE/dlinsolx.c b/EXAMPLE/dlinsolx.c
+index fdfd6727909f3308..271dd0b94815649c 100644
+--- a/EXAMPLE/dlinsolx.c
++++ b/EXAMPLE/dlinsolx.c
+@@ -18,6 +18,8 @@ at the top-level directory.
+  */
+ #include "slu_ddefs.h"
+ 
++#include <unistd.h>
++
+ int main(int argc, char *argv[])
+ {
+     char           equed[1];
+diff --git a/EXAMPLE/dlinsolx1.c b/EXAMPLE/dlinsolx1.c
+index e6993f956f31c5fe..7038ece2ac29aa46 100644
+--- a/EXAMPLE/dlinsolx1.c
++++ b/EXAMPLE/dlinsolx1.c
+@@ -20,6 +20,8 @@ at the top-level directory.
+  */
+ #include "slu_ddefs.h"
+ 
++#include <unistd.h>
++
+ int main(int argc, char *argv[])
+ {
+ /*
+diff --git a/EXAMPLE/dlinsolx2.c b/EXAMPLE/dlinsolx2.c
+index 7050f438a8f29a96..5d93b81d9871fb11 100644
+--- a/EXAMPLE/dlinsolx2.c
++++ b/EXAMPLE/dlinsolx2.c
+@@ -20,6 +20,8 @@ at the top-level directory.
+  */
+ #include "slu_ddefs.h"
+ 
++#include <unistd.h>
++
+ int main(int argc, char *argv[])
+ {
+ /*
+diff --git a/EXAMPLE/dlinsolx3.c b/EXAMPLE/dlinsolx3.c
+index 0a82c7bbea362a2d..bc51680e3ddc205d 100644
+--- a/EXAMPLE/dlinsolx3.c
++++ b/EXAMPLE/dlinsolx3.c
+@@ -20,6 +20,8 @@ at the top-level directory.
+  */
+ #include "slu_ddefs.h"
+ 
++#include <unistd.h>
++
+ int main(int argc, char *argv[])
+ {
+ /*
+diff --git a/EXAMPLE/sfgmr.c b/EXAMPLE/sfgmr.c
+index f2428200f0b27040..1358b5c95c2c1ff2 100644
+--- a/EXAMPLE/sfgmr.c
++++ b/EXAMPLE/sfgmr.c
+@@ -33,6 +33,8 @@ For information on ITSOL contact saad@cs.umn.edu
+ 
+ #define  epsmac  1.0e-16
+ 
++extern int scopy_(int *, float *, int *, float *, int *);
++extern void saxpy_(int *, float *, float *, int *, float *, int *);
+ extern float sdot_(int *, float [], int *, float [], int *);
+ extern float snrm2_(int *, float [], int *);
+ 
+diff --git a/EXAMPLE/slinsolx.c b/EXAMPLE/slinsolx.c
+index 32f1788b67bb3a28..9de609badc07c614 100644
+--- a/EXAMPLE/slinsolx.c
++++ b/EXAMPLE/slinsolx.c
+@@ -18,6 +18,8 @@ at the top-level directory.
+  */
+ #include "slu_sdefs.h"
+ 
++#include <unistd.h>
++
+ int main(int argc, char *argv[])
+ {
+     char           equed[1];
+diff --git a/EXAMPLE/slinsolx1.c b/EXAMPLE/slinsolx1.c
+index 2d9ab0875aba1ac6..c1726cb73f484747 100644
+--- a/EXAMPLE/slinsolx1.c
++++ b/EXAMPLE/slinsolx1.c
+@@ -20,6 +20,8 @@ at the top-level directory.
+  */
+ #include "slu_sdefs.h"
+ 
++#include <unistd.h>
++
+ int main(int argc, char *argv[])
+ {
+ /*
+diff --git a/EXAMPLE/slinsolx2.c b/EXAMPLE/slinsolx2.c
+index aca9dc13b405b48a..ad4a06f8ed906723 100644
+--- a/EXAMPLE/slinsolx2.c
++++ b/EXAMPLE/slinsolx2.c
+@@ -20,6 +20,8 @@ at the top-level directory.
+  */
+ #include "slu_sdefs.h"
+ 
++#include <unistd.h>
++
+ int main(int argc, char *argv[])
+ {
+ /*
+diff --git a/EXAMPLE/slinsolx3.c b/EXAMPLE/slinsolx3.c
+index cb3356cd48bd5df9..0aefbd90e698b992 100644
+--- a/EXAMPLE/slinsolx3.c
++++ b/EXAMPLE/slinsolx3.c
+@@ -20,6 +20,8 @@ at the top-level directory.
+  */
+ #include "slu_sdefs.h"
+ 
++#include <unistd.h>
++
+ int main(int argc, char *argv[])
+ {
+ /*
+diff --git a/EXAMPLE/sp_ienv.c b/EXAMPLE/sp_ienv.c
+index 266b4eeb59f9ee99..2a8d99f48080aa0e 100644
+--- a/EXAMPLE/sp_ienv.c
++++ b/EXAMPLE/sp_ienv.c
+@@ -23,7 +23,7 @@ at the top-level directory.
+  * File name:		sp_ienv.c
+  * History:             Modified from lapack routine ILAENV
+  */
+-#include "slu_Cnames.h"
++#include "slu_sdefs.h"
+ 
+ /*! \brief
+ 
+diff --git a/EXAMPLE/superlu.c b/EXAMPLE/superlu.c
+index fd42a6ad5ded236a..b32d7e697c76c8e4 100644
+--- a/EXAMPLE/superlu.c
++++ b/EXAMPLE/superlu.c
+@@ -20,7 +20,7 @@ at the top-level directory.
+  */
+ #include "slu_ddefs.h"
+ 
+-main(int argc, char *argv[])
++int main(int argc, char *argv[])
+ {
+ /*
+  * Purpose
+diff --git a/EXAMPLE/zfgmr.c b/EXAMPLE/zfgmr.c
+index 223a4f48ebe6f488..7d094dfbc0864d2c 100644
+--- a/EXAMPLE/zfgmr.c
++++ b/EXAMPLE/zfgmr.c
+@@ -33,6 +33,8 @@ For information on ITSOL contact saad@cs.umn.edu
+ 
+ #define  epsmac  1.0e-16
+ 
++extern int zcopy_(int *, doublecomplex *, int *, doublecomplex *, int *);
++extern void zaxpy_(int *, doublecomplex *, doublecomplex *, int *, doublecomplex *, int *);
+ extern void zdotc_(doublecomplex *, int *, doublecomplex [], int *, doublecomplex [], int *);
+ extern double dznrm2_(int *, doublecomplex [], int *);
+ 
+diff --git a/EXAMPLE/zlinsolx.c b/EXAMPLE/zlinsolx.c
+index 0540461dc043e2bc..bb2f3851aa57584d 100644
+--- a/EXAMPLE/zlinsolx.c
++++ b/EXAMPLE/zlinsolx.c
+@@ -18,6 +18,8 @@ at the top-level directory.
+  */
+ #include "slu_zdefs.h"
+ 
++#include <unistd.h>
++
+ int main(int argc, char *argv[])
+ {
+     char           equed[1];
+diff --git a/EXAMPLE/zlinsolx1.c b/EXAMPLE/zlinsolx1.c
+index badbf94cc33ca410..780e87cf594b9b1f 100644
+--- a/EXAMPLE/zlinsolx1.c
++++ b/EXAMPLE/zlinsolx1.c
+@@ -20,6 +20,8 @@ at the top-level directory.
+  */
+ #include "slu_zdefs.h"
+ 
++#include <unistd.h>
++
+ int main(int argc, char *argv[])
+ {
+ /*
+diff --git a/EXAMPLE/zlinsolx2.c b/EXAMPLE/zlinsolx2.c
+index 902c3535c3a905f5..579922433a7d2464 100644
+--- a/EXAMPLE/zlinsolx2.c
++++ b/EXAMPLE/zlinsolx2.c
+@@ -20,6 +20,8 @@ at the top-level directory.
+  */
+ #include "slu_zdefs.h"
+ 
++#include <unistd.h>
++
+ int main(int argc, char *argv[])
+ {
+ /*
+diff --git a/EXAMPLE/zlinsolx3.c b/EXAMPLE/zlinsolx3.c
+index 5080c03a34d6c7ae..a1763ed45ccbb028 100644
+--- a/EXAMPLE/zlinsolx3.c
++++ b/EXAMPLE/zlinsolx3.c
+@@ -20,6 +20,8 @@ at the top-level directory.
+  */
+ #include "slu_zdefs.h"
+ 
++#include <unistd.h>
++
+ int main(int argc, char *argv[])
+ {
+ /*
diff --git a/SuperLU.spec b/SuperLU.spec
index a52fb0a..8413236 100644
--- a/SuperLU.spec
+++ b/SuperLU.spec
@@ -3,7 +3,7 @@
 
 Name:		SuperLU
 Version:	5.3.0
-Release:	4%{?dist}
+Release:	5%{?dist}
 Summary:	Subroutines to solve sparse linear systems
 License:	BSD and GPLv2+
 URL:		https://portal.nersc.gov/project/sparse/superlu/
@@ -19,6 +19,7 @@ Patch1:		%{name}-set_soname.patch
 
 # Fix ldflags of example files
 Patch2:         %{name}-fix_example_builds.patch
+Patch3: SuperLU-c99.patch
 
 %if 0%{?fedora} >= 33
 BuildRequires: pkgconfig(flexiblas)
@@ -145,6 +146,9 @@ popd
 %doc DOC
 
 %changelog
+* Tue Feb 21 2023 Florian Weimer <fweimer@redhat.com> - 5.3.0-5
+- Port to C99
+
 * Wed Jan 18 2023 Fedora Release Engineering <releng@fedoraproject.org> - 5.3.0-4
 - Rebuilt for https://fedoraproject.org/wiki/Fedora_38_Mass_Rebuild