diff --git a/clang/include/clang/Basic/DiagnosticDriverKinds.td b/clang/include/clang/Basic/DiagnosticDriverKinds.td
--- a/clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ b/clang/include/clang/Basic/DiagnosticDriverKinds.td
@@ -253,6 +253,9 @@
   "support for '/Yc' with more than one source file not implemented yet; flag ignored">,
   InGroup<ClangClPch>;
 
+def warn_drv_potentially_misspelled_joined_argument : Warning<
+  "joined argument treated as '%0'; did you mean '%1'?">, InGroup<UnknownArgument>;
+
 def err_drv_invalid_value : Error<"invalid value '%1' in '%0'">;
 def err_drv_invalid_int_value : Error<"invalid integral value '%1' in '%0'">;
 def err_drv_invalid_value_with_suggestion : Error<
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -327,6 +327,19 @@
                      DiagnosticsEngine::Warning;
   }
 
+  for (const Arg *A : Args.filtered(options::OPT_o)) {
+    if (ArgStrings[A->getIndex()] == A->getSpelling())
+      continue;
+
+    // Warn on joined arguments that are similar to a long argument.
+    std::string ArgString = ArgStrings[A->getIndex()];
+    std::string Nearest;
+    if (getOpts().findNearest("-" + ArgString, Nearest, IncludedFlagsBitmask,
+                              ExcludedFlagsBitmask) == 0)
+      Diags.Report(diag::warn_drv_potentially_misspelled_joined_argument)
+          << A->getAsString(Args) << Nearest;
+  }
+
   return Args;
 }
 
diff --git a/clang/test/Driver/unknown-arg.c b/clang/test/Driver/unknown-arg.c
--- a/clang/test/Driver/unknown-arg.c
+++ b/clang/test/Driver/unknown-arg.c
@@ -64,3 +64,11 @@
 // RUN: %clang -S %s -o %t.s  -Wunknown-to-clang-option 2>&1 | FileCheck --check-prefix=IGNORED %s
 
 // IGNORED: warning: unknown warning option '-Wunknown-to-clang-option'
+
+// RUN: %clang -### -offload-arch=sm_70 --offload-arch=sm_70 -offload-device-only -o ffload-device-only \
+// RUN:   -output -o foo %s 2>&1 | FileCheck --check-prefix=O-WARN %s
+//      O-WARN: warning: joined argument treated as '-o ffload-arch=sm_70'; did you mean '--offload-arch=sm_70'?
+// O-WARN-NEXT: warning: joined argument treated as '-o ffload-device-only'; did you mean '--offload-device-only'?
+// O-WARN-NEXT: warning: joined argument treated as '-o utput'; did you mean '--output'?
+
+// RUN: %clang -### --offload-arch=sm_70 -o ffload-device-only -Werror=unknown-argument %s