diff --git a/cc65-c99.patch b/cc65-c99.patch
new file mode 100644
index 0000000..0dd9b49
--- /dev/null
+++ b/cc65-c99.patch
@@ -0,0 +1,17 @@
+Build test suite which is largely C89 with -std=gnu89.
+
+Submitted upstream: <https://github.com/cc65/cc65/issues/2277>
+
+diff --git a/test/ref/Makefile b/test/ref/Makefile
+index 5f0b86164d7145d7..42ca263efecbb832 100644
+--- a/test/ref/Makefile
++++ b/test/ref/Makefile
+@@ -38,7 +38,7 @@ OPTIONS = g O Os Osi Osir Osr Oi Oir Or
+ DIFF = $(WORKDIR)$Sbdiff$(EXE)
+ 
+ CC = gcc
+-CFLAGS = -O2 -Wall -W -Wextra -funsigned-char -fwrapv -fno-strict-overflow
++CFLAGS = -std=gnu89 -O2 -Wall -W -Wextra -funsigned-char -fwrapv -fno-strict-overflow
+ 
+ .PHONY: all clean
+ 
diff --git a/cc65.spec b/cc65.spec
index 7292779..d8da63b 100644
--- a/cc65.spec
+++ b/cc65.spec
@@ -43,7 +43,7 @@ infodir="%{_infodir}"
 
 Name:           cc65
 Version:        2.19
-Release:        7%{?dist}
+Release:        8%{?dist}
 Summary:        A free C compiler for 6502 based systems
 
 # For license clarification see:
@@ -51,6 +51,7 @@ Summary:        A free C compiler for 6502 based systems
 License:        zlib
 URL:            https://cc65.github.io
 Source0:        %{git_url}/archive/V%{version}/%{name}-%{version}.tar.gz
+Patch0: cc65-c99.patch
 
 # Backported from upstream.
 # none
@@ -266,6 +267,9 @@ they have been split into this package.
 
 
 %changelog
+* Wed Nov 29 2023 Florian Weimer <fweimer@redhat.com> - 2.19-8
+- Build testsuite reference in C89 mode
+
 * Thu Jul 20 2023 Dan Horák <dan[at]danny.cz> - 2.19-7
 - don't build docs in info format as a workaround (rhbz#2188018)