Index: Common/Args.cpp
===================================================================
--- Common/Args.cpp
+++ Common/Args.cpp
@@ -40,16 +40,16 @@
 
 uint64_t lld::args::getZOptionValue(opt::InputArgList &Args, int Id,
                                     StringRef Key, uint64_t Default) {
+  uint64_t Result = Default;
   for (auto *Arg : Args.filtered(Id)) {
     std::pair<StringRef, StringRef> KV = StringRef(Arg->getValue()).split('=');
     if (KV.first == Key) {
-      uint64_t Result = Default;
       if (!to_integer(KV.second, Result))
         error("invalid " + Key + ": " + KV.second);
-      return Result;
+      Arg->claim();
     }
   }
-  return Default;
+  return Result;
 }
 
 std::vector<StringRef> lld::args::getLines(MemoryBufferRef MB) {
Index: ELF/Driver.cpp
===================================================================
--- ELF/Driver.cpp
+++ ELF/Driver.cpp
@@ -307,7 +307,15 @@
   return getenv("LLD_REPRODUCE");
 }
 
+static void claimZOptions(opt::InputArgList &Args, ArrayRef<StringRef> Keys) {
+  for (auto *Arg : Args.filtered(OPT_z))
+    for (StringRef K : Keys)
+      if (Arg->getValue() == K)
+        Arg->claim();
+}
+
 static bool hasZOption(opt::InputArgList &Args, StringRef Key) {
+  claimZOptions(Args, {Key});
   for (auto *Arg : Args.filtered(OPT_z))
     if (Key == Arg->getValue())
       return true;
@@ -316,6 +324,7 @@
 
 static bool getZFlag(opt::InputArgList &Args, StringRef K1, StringRef K2,
                      bool Default) {
+  claimZOptions(Args, {K1, K2});
   for (auto *Arg : Args.filtered_reverse(OPT_z)) {
     if (K1 == Arg->getValue())
       return true;
@@ -417,6 +426,8 @@
 // Determines what we should do if there are remaining unresolved
 // symbols after the name resolution.
 static UnresolvedPolicy getUnresolvedSymbolPolicy(opt::InputArgList &Args) {
+  claimZOptions(Args, {"defs"});
+
   if (Args.hasArg(OPT_relocatable))
     return UnresolvedPolicy::IgnoreAll;
 
@@ -679,9 +690,9 @@
   ThreadsEnabled = Args.hasFlag(OPT_threads, OPT_no_threads, true);
 
   Config->AllowMultipleDefinition =
+      hasZOption(Args, "muldefs") ||
       Args.hasFlag(OPT_allow_multiple_definition,
-                   OPT_no_allow_multiple_definition, false) ||
-      hasZOption(Args, "muldefs");
+                   OPT_no_allow_multiple_definition, false);
   Config->AuxiliaryList = args::getStrings(Args, OPT_auxiliary);
   Config->Bsymbolic = Args.hasArg(OPT_Bsymbolic);
   Config->BsymbolicFunctions = Args.hasArg(OPT_Bsymbolic_functions);
@@ -1205,6 +1216,10 @@
   Config->MaxPageSize = getMaxPageSize(Args);
   Config->ImageBase = getImageBase(Args);
 
+  for (auto *Arg : Args.filtered(OPT_z))
+    if (!Arg->isClaimed())
+      warn("unknown -z value: " + StringRef(Arg->getValue()));
+
   // If a -hash-style option was not given, set to a default value,
   // which varies depending on the target.
   if (!Args.hasArg(OPT_hash_style)) {
Index: test/ELF/invalid-z.s
===================================================================
--- test/ELF/invalid-z.s
+++ test/ELF/invalid-z.s
@@ -4,6 +4,10 @@
 # CHECK: invalid max-page-size
 # CHECK-NOT: error
 
+# RUN: ld.lld %t.o -o %t -z foobar 2>&1 | \
+# RUN:   FileCheck %s --check-prefix=UNKNOWN
+# UNKNOWN: warning: unknown -z value: foobar
+
 .global _start
 _start:
   nop