diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 47b01a3fac..e3de29d6ac 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -40,9 +40,6 @@ add_subdirectory(unit)
 add_subdirectory(certs EXCLUDE_FROM_ALL)
 
 function(curl_add_runtests _targetname _test_flags)
-  if(CURL_TEST_BUNDLES)
-    string(APPEND _test_flags " -bundle")
-  endif()
   if(NOT BUILD_LIBCURL_DOCS)
     string(APPEND _test_flags " !documentation")
   endif()
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 1707d6eb97..eec55ab909 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -123,9 +123,6 @@ if CROSSCOMPILING
 TEST = @echo "NOTICE: we can't run the tests when cross-compiling!"
 PYTEST = $(TEST)
 else # if not cross-compiling:
-if USE_TEST_BUNDLES
-TEST_COMMON += -bundle
-endif
 
 if BUILD_DOCS
 else
diff --git a/tests/runner.pm b/tests/runner.pm
index 633a927bcf..7f379f42a1 100644
--- a/tests/runner.pm
+++ b/tests/runner.pm
@@ -916,24 +916,20 @@ sub singletest_run {
         # Default the tool to a unit test with the same name as the test spec
         if($keywords{"unittest"} && !$tool) {
             $tool_name="unit$testnum";
-            $tool = $tool_name;
+            $tool = $tool_name . exe_ext('TOOL');
         }
 
         if($tool =~ /^lib/) {
             if($bundle) {
-                $CMDLINE=$LIBDIR . "libtests";
-            }
-            else {
-                $CMDLINE=$LIBDIR . $tool;
+                $tool = "libtests" . exe_ext('TOOL');
             }
+            $CMDLINE=$LIBDIR . $tool;
         }
         elsif($tool =~ /^unit/) {
             if($bundle) {
-                $CMDLINE=$UNITDIR . "units";
-            }
-            else {
-                $CMDLINE=$UNITDIR . $tool;
+                $tool = "units" . exe_ext('TOOL')
             }
+            $CMDLINE=$UNITDIR . $tool;
         }
 
         if(! -f $CMDLINE) {
diff --git a/tests/runtests.md b/tests/runtests.md
index ef6b012eba..2c875440d7 100644
--- a/tests/runtests.md
+++ b/tests/runtests.md
@@ -96,11 +96,6 @@ Provide a path to a curl binary to talk to APIs (currently only CI test APIs).
 
 Display test results in automake style output (`PASS/FAIL: [number] [name]`).
 
-## `-bundle`
-
-Run tests via bundled test binaries. Bundled test binaries contain all tests,
-and the test name passed as the first argument selects which test run.
-
 ## `-c \<curl\>`
 
 Provide a path to a custom curl binary to run the tests with. Default is the
diff --git a/tests/runtests.pl b/tests/runtests.pl
index e23f809eff..f360920b02 100755
--- a/tests/runtests.pl
+++ b/tests/runtests.pl
@@ -88,6 +88,7 @@ use serverhelp qw(
     server_exe
     );
 use pathhelp qw(
+    exe_ext
     sys_native_current_path
     );
 use processhelp qw(
@@ -2280,11 +2281,6 @@ while(@ARGV) {
         $ACURL=shell_quote($ARGV[1]);
         shift @ARGV;
     }
-    elsif ($ARGV[0] eq "-bundle") {
-        # use test bundles
-        $bundle=1;
-        $ENV{'CURL_TEST_BUNDLES'} = 1;
-    }
     elsif ($ARGV[0] eq "-d") {
         # have the servers display protocol output
         $debugprotocol=1;
@@ -2466,7 +2462,6 @@ Usage: runtests.pl [options] [test selection(s)]
   -a       continue even if a test fails
   -ac path use this curl only to talk to APIs (currently only CI test APIs)
   -am      automake style output PASS/FAIL: [number] [name]
-  -bundle  use test bundles
   -c path  use this curl executable
   -d       display server debug info
   -e, --test-event  event-based execution
@@ -2546,6 +2541,15 @@ EOHELP
     shift @ARGV;
 }
 
+# Detect a test bundle build
+if(-e $LIBDIR . "libtests" . exe_ext('TOOL') &&
+   -e $UNITDIR . "units" . exe_ext('TOOL') &&
+   -e $SRVDIR . "servers" . exe_ext('SRV')) {
+    # use test bundles
+    $bundle=1;
+    $ENV{'CURL_TEST_BUNDLES'} = 1;
+}
+
 delete $ENV{'DEBUGINFOD_URLS'} if($ENV{'DEBUGINFOD_URLS'} && $no_debuginfod);
 
 if(!$randseed) {