diff --git a/libbuild2-autoconf-tests/basics/testscript b/libbuild2-autoconf-tests/basics/testscript
index 6c0c471..0e7612d 100644
--- a/libbuild2-autoconf-tests/basics/testscript
+++ b/libbuild2-autoconf-tests/basics/testscript
@@ -92,7 +92,7 @@ cat config.h >>EOO
 :
 mkdir build;
 ln -s ../../bootstrap.build ../../root.build build/;
-cat <<EOI >=config.h.in;
+cat <<EOI >=config.h.cmake;
   #define VERSION "@version@"
 
   #cmakedefine TRUE
@@ -115,10 +115,8 @@ cat <<EOI >=config.h.in;
   #cmakedefine zzz_TEST_DUMMY2_H
   EOI
 $* <<EOI &config.h &config.h.d;
-  ./: h{config}: in{config}
+  ./: h{config}: in{config.h.cmake}
   {
-    autoconf.flavor = cmake
-
     TRUE  = true
     FALSE = [bool] false
     ONE   = 1
diff --git a/libbuild2-autoconf/libbuild2/autoconf/buildfile b/libbuild2-autoconf/libbuild2/autoconf/buildfile
index 9cf1ec6..62f1ebc 100644
--- a/libbuild2-autoconf/libbuild2/autoconf/buildfile
+++ b/libbuild2-autoconf/libbuild2/autoconf/buildfile
@@ -60,8 +60,6 @@ lib{build2-autoconf}: {hxx ixx txx cxx}{* -checks} {hxx cxx}{checks} \
   \"\"
   EOI
 
-  # @@ TODO: add \n once sed supports it.
-  #
   cat $i | sed -n \
     -e 's|^// ([^ ]+) *$|},\n\n{\n"\1",\n|p' \
     -e 's|^(.*)\\$|"\1\\\\\\n"|p' \
diff --git a/libbuild2-autoconf/libbuild2/autoconf/rule.cxx b/libbuild2-autoconf/libbuild2/autoconf/rule.cxx
index 2a969aa..82d863c 100644
--- a/libbuild2-autoconf/libbuild2/autoconf/rule.cxx
+++ b/libbuild2-autoconf/libbuild2/autoconf/rule.cxx
@@ -4,6 +4,8 @@
 #include <libbuild2/algorithm.hxx>
 #include <libbuild2/diagnostics.hxx>
 
+#include <libbuild2/in/target.hxx>
+
 #include <libbuild2/autoconf/checks.hxx>
 
 using namespace std;
@@ -34,22 +36,44 @@ namespace build2
     recipe rule::
     apply (action a, target& t) const
     {
+      recipe r (in::rule::apply (a, t));
+
       // Determine and cache the configuration file flavor.
       //
       flavor f (flavor::autoconf);
+
       if (const string* s = cast_null<string> (t["autoconf.flavor"]))
       {
-        if (*s == "cmake")
-          f = flavor::cmake;
-        else if (*s == "meson")
-          f = flavor::meson;
+        if      (*s == "cmake") f = flavor::cmake;
+        else if (*s == "meson") f = flavor::meson;
         else if (*s != "autoconf")
           fail << "invalid configuration file flavor '" << *s << "'";
       }
+      else
+      {
+        // If the in{} file extension is either .cmake or .meson, then
+        // use that as the flavor.
+        //
+        for (const target* pt: t.prerequisite_targets[a])
+        {
+          if (pt != nullptr)
+          {
+            if (const auto* it = pt->is_a<in::in> ())
+            {
+              string e (it->path ().extension ());
+
+              if      (e == "cmake") f = flavor::cmake;
+              else if (e == "meson") f = flavor::meson;
+
+              break;
+            }
+          }
+        }
+      }
 
       t.data (match_data {f});
 
-      return in::rule::apply (a, t);
+      return r;
     }
 
     void rule::
diff --git a/libbuild2-autoconf/libbuild2/autoconf/rule.hxx b/libbuild2-autoconf/libbuild2/autoconf/rule.hxx
index 1318224..626e991 100644
--- a/libbuild2-autoconf/libbuild2/autoconf/rule.hxx
+++ b/libbuild2-autoconf/libbuild2/autoconf/rule.hxx
@@ -9,7 +9,7 @@ namespace build2
 {
   namespace autoconf
   {
-    // Process a config.h.in file.
+    // Process a config.h.{in,cmake,meson} file.
     //
     // Note that to be usable as a drop-in replacement we make the default
     // substitution symbol '@' and the mode -- lax. The user, however, is