diff --git a/libdbus-c++.changes b/libdbus-c++.changes
index 63c6c13..be172ab 100644
--- a/libdbus-c++.changes
+++ b/libdbus-c++.changes
@@ -1,3 +1,10 @@
+-------------------------------------------------------------------
+Fri Nov 22 00:37:29 UTC 2019 - Stefan Brüns <stefan.bruens@rwth-aachen.de>
+
+- Drop -Werror=date-time, it is not supported by older GCCs, and
+  newer ones support SOURCE_DATE_EPOCH
+- Conflict older devel packages, to avoid file conflicts.
+
 -------------------------------------------------------------------
 Thu Nov 21 00:54:46 UTC 2019 - Stefan Brüns <stefan.bruens@rwth-aachen.de>
 
diff --git a/libdbus-c++.spec b/libdbus-c++.spec
index 09f130e..912b9c7 100644
--- a/libdbus-c++.spec
+++ b/libdbus-c++.spec
@@ -101,6 +101,7 @@ Summary:        Development files for libdbus-c++
 Group:          Development/Libraries/C and C++
 Requires:       libdbus-c++%{?psuffix}-1-%{sover} = %{version}
 Recommends:     libdbus-c++-api-docs
+Conflicts:      libdbus-c++-devel <= %{version}-%{release}
 
 %description devel
 DBus-c++ provides a C++ API for D-BUS. The library has
@@ -120,21 +121,21 @@ libdbus-c++.
 %build
 export SOVER="%{sover}:0:0"
 export LDFLAGS="$LDFLAGS -lexpat -lpthread -pie"
-export CFLAGS="%{optflags} -fPIC -Werror=date-time"
-export CXXFLAGS="%{optflags} --std=c++11 -fPIC -Werror=date-time"
+export CFLAGS="%{optflags} -fPIC"
+export CXXFLAGS="%{optflags} --std=c++11 -fPIC"
 ./bootstrap
 %configure \
-           --disable-ecore \
-           --enable-static=no \
+        --disable-ecore \
+        --enable-static=no \
 %if %{without glib}
-           --disable-glib \
+        --disable-glib \
 %endif
 %if %{with docs}
-	   --enable-doxygen-docs \
+        --enable-doxygen-docs \
 %else
-           --disable-doxygen-docs \
-           --enable-tests \
-	   --enable-examples
+        --disable-doxygen-docs \
+        --enable-tests \
+        --enable-examples
 %endif
 
 %if "%{flavor}" == "docs"