diff --git a/pkgs/development/libraries/spandsp/common.nix b/pkgs/development/libraries/spandsp/common.nix
index 317e5494f790..1aacb0f1123f 100644
--- a/pkgs/development/libraries/spandsp/common.nix
+++ b/pkgs/development/libraries/spandsp/common.nix
@@ -45,12 +45,18 @@ stdenv.mkDerivation (finalAttrs: {
 
   postPatch = ''
     patchShebangs autogen.sh
-
-    # pkg-config? What's that?
-    # Actually *check* the value given for --{en,dis}able-tests, not just whether the option was passed
+  ''
+  # pkg-config? What's that?
+  # Actually *check* the value given for --{en,dis}able-tests, not just whether the option was passed
+  + ''
     substituteInPlace configure.ac \
       --replace-fail '$xml2_include_dir /usr/include /usr/local/include /usr/include/libxml2 /usr/local/include/libxml2' '$xml2_include_dir ${lib.getDev libxml2}/include ${lib.getDev libxml2}/include/libxml2 /usr/local/include/libxml2' \
       --replace-fail 'if test -n "$enable_tests" ; then' 'if test "$enable_tests" = "yes" ; then'
+  ''
+  # Don't install generated test data
+  + ''
+    substituteInPlace test-data/{etsi,itu}/fax/Makefile.am \
+      --replace-fail 'nobase_data_DATA' 'noinst_DATA'
   '';
 
   outputs = [