diff --git a/unbound-1.15-source-compat.patch b/unbound-1.15-source-compat.patch
new file mode 100644
index 0000000..fc0ce0e
--- /dev/null
+++ b/unbound-1.15-source-compat.patch
@@ -0,0 +1,57 @@
+From 4c099ddf17d0c3a0ccaffd0d85281dde4f16d0b1 Mon Sep 17 00:00:00 2001
+From: Petr Mensik <pemensik@redhat.com>
+Date: Sat, 7 May 2022 10:05:33 +0200
+Subject: [PATCH] Use reserved RCODE, fake source version
+
+Use RCODE value assigned for a private use. Previous value were possible
+returned value.
+
+Fake source version to be still 1.7.x. Hide real version into micro
+version component and export it also in a proper way with _REAL
+suffixes. Should workaround any source code detection to support correct
+callback format. Fixes compilation error in libreswan.
+---
+ libunbound/unbound.h | 13 ++++++++++---
+ services/mesh.h      |  2 +-
+ 2 files changed, 11 insertions(+), 4 deletions(-)
+
+diff --git a/libunbound/unbound.h b/libunbound/unbound.h
+index c822d3f89..2dbb9a358 100644
+--- a/libunbound/unbound.h
++++ b/libunbound/unbound.h
+@@ -102,9 +102,16 @@ extern "C" {
+ #endif
+ 
+ /** the version of this header file */
+-#define UNBOUND_VERSION_MAJOR @UNBOUND_VERSION_MAJOR@
+-#define UNBOUND_VERSION_MINOR @UNBOUND_VERSION_MINOR@
+-#define UNBOUND_VERSION_MICRO @UNBOUND_VERSION_MICRO@
++/* Because of RHEL compat change, callback type remains at
++ * 1.7.3 version. To prevent source-level incompatibility,
++ * fake still old version. Export real version in _REAL
++ * suffix definitions. */
++#define UNBOUND_VERSION_MAJOR 1
++#define UNBOUND_VERSION_MINOR 7
++#define UNBOUND_VERSION_MICRO @UNBOUND_VERSION_MAJOR@@UNBOUND_VERSION_MINOR@
++#define UNBOUND_VERSION_MAJOR_REAL @UNBOUND_VERSION_MAJOR@
++#define UNBOUND_VERSION_MINOR_REAL @UNBOUND_VERSION_MINOR@
++#define UNBOUND_VERSION_MICRO_REAL @UNBOUND_VERSION_MICRO@
+ 
+ /**
+  * The validation context is created to hold the resolver status,
+diff --git a/services/mesh.h b/services/mesh.h
+index 9c6f958ff..c0cbf355e 100644
+--- a/services/mesh.h
++++ b/services/mesh.h
+@@ -237,7 +237,7 @@ struct mesh_reply {
+ /* RHEL 8 compatibility layer.
+  * Special rcode to send was_ratelimited to callback without adding
+  * extra parameter. It is ORed to the rcode parameter of the callback. */
+-#define LDNS_RCODE_RATELIMITED 0x100
++#define LDNS_RCODE_RATELIMITED 0xf80
+ #define RCODE_IS_RATELIMITED(rcode) ((rcode & LDNS_RCODE_RATELIMITED) != 0)
+ #define RCODE_NOT_RATELIMITED(rcode) (rcode & ~LDNS_RCODE_RATELIMITED)
+ 
+-- 
+2.34.1
+
diff --git a/unbound.spec b/unbound.spec
index 838df3d..a831ade 100644
--- a/unbound.spec
+++ b/unbound.spec
@@ -55,7 +55,10 @@ Source18: https://nlnetlabs.nl/downloads/%{name}/%{name}-%{version}%{?extra_vers
 # source: https://nlnetlabs.nl/people/
 Source19: https://keys.openpgp.org/pks/lookup?op=get&search=0x9F6F1C2D7E045F8D#/wouter.nlnetlabs.nl.key
 
+# Reverts ABI change done in version 1.8.0 (bz#2027735)
+# Makes possible backward binary compatibility with a new features
 Patch1:   unbound-1.15-soversion2-compat.patch
+Patch2:   unbound-1.15-source-compat.patch
 
 BuildRequires: gcc, make
 BuildRequires: flex, openssl-devel
@@ -450,6 +453,7 @@ popd
 %changelog
 * Fri May 06 2022 Petr Menšík <pemensik@redhat.com> - 1.15.0-4
 - Update to recent version with compatibility with RHEL8 (#2027735)
+- Ensure also source level compatibility with previous version
 
 * Tue Apr 26 2022 Petr Menšík <pemensik@redhat.com> - 1.15.0-3
 - Stop creating wrong devel manual pages (#2078929)