diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6efd5b4a..1fcef169 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -42,3 +42,16 @@ jobs:
       - name: Unit tests (IPv4)
         if: ${{ !cancelled() }}
         run: cd test && ./unit --ipv4
+
+      # Build the files that util/strip.py writes for upstreaming, which
+      # nothing else here compiles. --kernel keeps the code for this kernel
+      # in LINUX_VERSION_CODE blocks so that they build with it. -Werror
+      # makes stripping mistakes such as a dangling "else" fail.
+      - name: Build homa.ko from util/strip.py output
+        if: ${{ !cancelled() }}
+        run: |
+          out=$RUNNER_TEMP/net-next
+          mkdir -p $out/net $out/include/uapi/linux
+          make net-next LINUX_SRC_DIR=$out "STRIP_FLAGS=--kernel $LINUX_VERSION"
+          make -C $KDIR M=$out/net/homa CONFIG_HOMA=m KBUILD_MODPOST_WARN=1 \
+            KCFLAGS="-I$out/include/uapi -Werror" modules
diff --git a/Makefile b/Makefile
index 8c8f17f9..e40a5796 100644
--- a/Makefile
+++ b/Makefile
@@ -83,7 +83,7 @@ net-next: $(HOMA_TARGET) $(CP_TARGETS) $(LINUX_SRC_DIR)/include/uapi/linux/homa.
 $(HOMA_TARGET):
 	mkdir $(HOMA_TARGET)
 $(HOMA_TARGET)/%: % util/strip.py
-	util/strip.py $< > $@
+	util/strip.py $(STRIP_FLAGS) $< > $@
 $(HOMA_TARGET)/%.txt: %.txt
 	cp $< $@
 $(HOMA_TARGET)/Makefile: Makefile.upstream
@@ -91,7 +91,7 @@ $(HOMA_TARGET)/Makefile: Makefile.upstream
 $(HOMA_TARGET)/strip_decl.py: util/strip_decl.py
 	cp $< $@
 $(LINUX_SRC_DIR)/include/uapi/linux/homa.h: homa.h util/strip.py
-	util/strip.py $< > $@
+	util/strip.py $(STRIP_FLAGS) $< > $@
 
 clean:
 	$(MAKE) -C $(KDIR) M=$(shell pwd) clean
diff --git a/util/strip.py b/util/strip.py
index be80dbc7..9f472b97 100755
--- a/util/strip.py
+++ b/util/strip.py
@@ -7,12 +7,17 @@
 a Linux kernel repo, removing information that doesn't belong in the
 official kernel version (such as calls to tt_record).
 
-Usage: strip.py file file file ... destdir
+Usage: strip.py [--kernel X.Y.Z] file file file ... destdir
 
 Each of the files will be read, stripped as appropriate, and copied to a
 file by the same name in destdir. If there is only a single file and no
 destdir, then the stripped file is printed on standard output.
 
+Normally only the #else code of an '#if LINUX_VERSION_CODE' block is kept.
+With --kernel, the code for that Linux version is kept instead, so that the
+stripped files can be compiled against the kernel that the main branch is
+built with (for testing only; this is not what goes upstream).
+
 The following code is removed automatically:
   * Calls to timetracing, such as tt_record*
   * Blocks conditionalized on '#ifdef __UNIT_TEST__'
@@ -141,6 +146,26 @@ def blank_next_ok(line: str) -> bool:
         return False
     return True
 
+# Linux version for --kernel, as a (major, minor, patch) tuple, or None.
+kernel = None
+
+def version_test(file: str, line_num: int, line: str) -> bool:
+    """
+    Return the value of an '#if LINUX_VERSION_CODE' test for kernel.
+    """
+
+    global exit_code
+
+    m = re.match(r'#if LINUX_VERSION_CODE\s*(<|>=)\s*'
+                 r'KERNEL_VERSION\((\d+),\s*(\d+),\s*(\d+)\)', line)
+    if not m:
+        print('%s:%d: can\'t evaluate %s' % (file, line_num, line.strip()),
+              file=sys.stderr)
+        exit_code = 1
+        return False
+    version = tuple(int(m.group(i)) for i in range(2, 5))
+    return (kernel < version) == (m.group(1) == '<')
+
 def scan(file: str) -> list[str]:
     """
     Read a file, remove information that shouldn't appear in the Linux kernel
@@ -179,6 +204,10 @@ def scan(file: str) -> list[str]:
     #          '#if LINUX_VERSION_CODE' (this code should remain)
     in_version = None
 
+    # Which part of the current '#if LINUX_VERSION_CODE' block to keep:
+    # 'if' or 'else'.
+    keep_version = 'else'
+
     # Array of lines containing the stripped version of the file
     slines = []
 
@@ -354,10 +383,14 @@ def scan(file: str) -> list[str]:
             if line.startswith('#else'):
                 in_version = 'else'
                 continue
-            if in_version == 'if':
+            if in_version != keep_version:
                 continue
         elif line.startswith('#if LINUX_VERSION_CODE'):
             in_version = 'if'
+            if kernel and version_test(file, line_num, line):
+                keep_version = 'if'
+            else:
+                keep_version = 'else'
             if not blank_next_ok(slines[-1]):
                 delete_empty_line = True
             continue
@@ -410,15 +443,20 @@ def scan(file: str) -> list[str]:
 
 if __name__ == '__main__':
     f = sys.stdin
-    if len(sys.argv) < 2:
-        print('Usage: strip.py [--alt] file [file ... destdir]', file=sys.stderr)
+    args = sys.argv[1:]
+    if len(args) > 1 and args[0] == '--kernel':
+        kernel = tuple(int(x) for x in args[1].split('.')[:3])
+        args = args[2:]
+    if len(args) < 1:
+        print('Usage: strip.py [--kernel X.Y.Z] file [file ... destdir]',
+              file=sys.stderr)
         exit(1)
-    if len(sys.argv) == 2:
-        for line in scan(sys.argv[1]):
+    if len(args) == 1:
+        for line in scan(args[0]):
             print(line, end='')
     else:
-        for file in sys.argv[1:-1]:
-            dst_file = '%s/%s' % (sys.argv[-1], file)
+        for file in args[:-1]:
+            dst_file = '%s/%s' % (args[-1], file)
             print('Stripping %s into %s' % (file, dst_file))
             slines = scan(file)
             dst = open(dst_file, 'w')