diff --git a/third_party/chibicc/as.c b/third_party/chibicc/as.c
index e05283875..4fe77a26f 100644
--- a/third_party/chibicc/as.c
+++ b/third_party/chibicc/as.c
@@ -3944,7 +3944,7 @@ static void Objectify(struct As *a, int path) {
   char *p;
   int i, j, s, e;
   struct ElfWriter *elf;
-  elf = elfwriter_open(a->strings.p[path], 0644);
+  elf = elfwriter_open(a->strings.p[path], 0644, EM_NEXGEN32E);
   for (i = 0; i < a->symbols.n; ++i) {
     if (!IsLiveSymbol(a, i)) continue;
     p = strndup(a->slices.p[a->symbols.p[i].name].p,
diff --git a/third_party/python/pyobj.c b/third_party/python/pyobj.c
index 26aca6d11..4367b22a0 100644
--- a/third_party/python/pyobj.c
+++ b/third_party/python/pyobj.c
@@ -646,7 +646,7 @@ Objectify(void)
     memcpy(pycdata + sizeof(header), mardata, marsize);
     yoinked = newinterner();
     forcepulls = newinterner();
-    elf = elfwriter_open(outpath, 0644);
+    elf = elfwriter_open(outpath, 0644, 0);
     elfwriter_cargoculting(elf);
     if (ispkg) {
         elfwriter_zip(elf, zipdir, zipdir, strlen(zipdir),
diff --git a/tool/build/lib/elfwriter.c b/tool/build/lib/elfwriter.c
index 6af6d849c..20b4a7748 100644
--- a/tool/build/lib/elfwriter.c
+++ b/tool/build/lib/elfwriter.c
@@ -156,7 +156,7 @@ static void FlushTables(struct ElfWriter *elf) {
   elfwriter_commit(elf, size);
 }
 
-struct ElfWriter *elfwriter_open(const char *path, int mode) {
+struct ElfWriter *elfwriter_open(const char *path, int mode, int arch) {
   struct ElfWriter *elf;
   CHECK_NOTNULL((elf = calloc(1, sizeof(struct ElfWriter))));
   CHECK_NOTNULL((elf->path = strdup(path)));
@@ -166,15 +166,22 @@ struct ElfWriter *elfwriter_open(const char *path, int mode) {
                                         elf->mapsize, PROT_READ | PROT_WRITE,
                                         MAP_SHARED | MAP_FIXED, elf->fd, 0)));
   elf->ehdr = memcpy(elf->map, &kObjHeader, (elf->wrote = sizeof(kObjHeader)));
-  if (strstr(path, "/aarch64")) {
-    elf->ehdr->e_machine = EM_AARCH64;
-  } else if (strstr(path, "/powerpc64")) {
-    elf->ehdr->e_machine = EM_PPC64;
-  } else if (strstr(path, "/riscv")) {
-    elf->ehdr->e_machine = EM_RISCV;
-  } else if (strstr(path, "/s390")) {
+  if (!arch) {
+#ifdef __x86_64__
+    arch = EM_NEXGEN32E;
+#elif defined(__aarch64__)
+    arch = EM_AARCH64;
+#elif defined(__powerpc64__)
+    arch = EM_PPC64;
+#elif defined(__riscv)
+    arch = EM_RISCV;
+#elif defined(__s390x__)
     elf->ehdr->e_machine = EM_S390;
+#else
+#error "unsupported architecture"
+#endif
   }
+  elf->ehdr->e_machine = arch;
   elf->strtab = newinterner();
   elf->shstrtab = newinterner();
   intern(elf->strtab, "");
diff --git a/tool/build/lib/elfwriter.h b/tool/build/lib/elfwriter.h
index 4a9c8439c..5bed297be 100644
--- a/tool/build/lib/elfwriter.h
+++ b/tool/build/lib/elfwriter.h
@@ -54,7 +54,7 @@ struct ElfWriter {
   struct Interner *shstrtab;
 };
 
-struct ElfWriter *elfwriter_open(const char *, int) __wur;
+struct ElfWriter *elfwriter_open(const char *, int, int) __wur;
 void elfwriter_cargoculting(struct ElfWriter *);
 void elfwriter_close(struct ElfWriter *);
 void elfwriter_align(struct ElfWriter *, size_t, size_t);
diff --git a/tool/build/zipobj.c b/tool/build/zipobj.c
index b9cac3fc9..7d09a9300 100644
--- a/tool/build/zipobj.c
+++ b/tool/build/zipobj.c
@@ -43,6 +43,7 @@
 #include "tool/build/lib/elfwriter.h"
 #include "tool/build/lib/stripcomponents.h"
 
+int arch_;
 char *name_;
 char *yoink_;
 char *symbol_;
@@ -76,6 +77,7 @@ FLAGS\n\
   -o PATH         output path\n\
   -0              disable compression\n\
   -B              basename-ify zip filename\n\
+  -a ARCH         microprocessor architecture\n\
   -N ZIPPATH      zip filename (defaults to input arg)\n\
   -P ZIPPATH      prepend path zip filename using join\n\
   -C INTEGER      strips leading path components from zip filename\n\
@@ -86,14 +88,34 @@ FLAGS\n\
   exit(rc);
 }
 
+static int ParseArch(const char *s) {
+  if (startswith(s, "x86")) {
+    return EM_NEXGEN32E;
+  } else if (startswith(s, "arm") || !strcmp(s, "aarch64")) {
+    return EM_AARCH64;
+  } else if (startswith(s, "ppc") || startswith(s, "powerpc")) {
+    return EM_PPC64;
+  } else if (startswith(s, "riscv")) {
+    return EM_RISCV;
+  } else if (startswith(s, "s390")) {
+    return EM_S390;
+  } else {
+    tinyprint(2, "error: unrecognized microprocessor architecture\n", NULL);
+    exit(1);
+  }
+}
+
 void GetOpts(int *argc, char ***argv) {
   int opt;
   yoink_ = "__zip_eocd";
-  while ((opt = getopt(*argc, *argv, "?0nhBN:C:P:o:s:y:")) != -1) {
+  while ((opt = getopt(*argc, *argv, "?0nhBN:C:P:o:s:y:a:")) != -1) {
     switch (opt) {
       case 'o':
         outpath_ = optarg;
         break;
+      case 'a':
+        arch_ = ParseArch(optarg);
+        break;
       case 'n':
         exit(0);
       case 's':
@@ -192,18 +214,18 @@ void PullEndOfCentralDirectoryIntoLinkage(struct ElfWriter *elf) {
 }
 
 void CheckFilenameKosher(const char *path) {
-  CHECK_LE(kZipCfileHdrMinSize + strlen(path), 65535);
-  CHECK(!startswith(path, "/"));
-  CHECK(!strstr(path, ".."));
+  unassert(kZipCfileHdrMinSize + strlen(path) <= 65535);
+  unassert(!startswith(path, "/"));
+  unassert(!strstr(path, ".."));
 }
 
 void zipobj(int argc, char **argv) {
   size_t i;
   struct ElfWriter *elf;
-  CHECK_LT(argc, UINT16_MAX / 3 - 64); /* ELF 64k section limit */
+  unassert(argc < UINT16_MAX / 3 - 64); /* ELF 64k section limit */
   GetOpts(&argc, &argv);
   for (i = 0; i < argc; ++i) CheckFilenameKosher(argv[i]);
-  elf = elfwriter_open(outpath_, 0644);
+  elf = elfwriter_open(outpath_, 0644, arch_);
   elfwriter_cargoculting(elf);
   for (i = 0; i < argc; ++i) ProcessFile(elf, argv[i]);
   PullEndOfCentralDirectoryIntoLinkage(elf);
@@ -211,7 +233,6 @@ void zipobj(int argc, char **argv) {
 }
 
 int main(int argc, char **argv) {
-  ShowCrashReports();
   timestamp.tv_sec = 1647414000; /* determinism */
   /* clock_gettime(CLOCK_REALTIME, &timestamp); */
   zipobj(argc, argv);