diff --git a/clang/lib/Driver/ToolChains/WebAssembly.cpp b/clang/lib/Driver/ToolChains/WebAssembly.cpp
--- a/clang/lib/Driver/ToolChains/WebAssembly.cpp
+++ b/clang/lib/Driver/ToolChains/WebAssembly.cpp
@@ -141,7 +141,7 @@
                          options::OPT_fno_use_init_array, true))
     CC1Args.push_back("-fuse-init-array");
 
-  // '-pthread' implies atomics, bulk-memory, and mutable-globals
+  // '-pthread' implies atomics, bulk-memory, mutable-globals, and sign-ext
   if (DriverArgs.hasFlag(options::OPT_pthread, options::OPT_no_pthread,
                          false)) {
     if (DriverArgs.hasFlag(options::OPT_mno_atomics, options::OPT_matomics,
@@ -159,12 +159,19 @@
       getDriver().Diag(diag::err_drv_argument_not_allowed_with)
           << "-pthread"
           << "-mno-mutable-globals";
+    if (DriverArgs.hasFlag(options::OPT_mno_sign_ext, options::OPT_msign_ext,
+                           false))
+      getDriver().Diag(diag::err_drv_argument_not_allowed_with)
+          << "-pthread"
+          << "-mno-sign-ext";
     CC1Args.push_back("-target-feature");
     CC1Args.push_back("+atomics");
     CC1Args.push_back("-target-feature");
     CC1Args.push_back("+bulk-memory");
     CC1Args.push_back("-target-feature");
     CC1Args.push_back("+mutable-globals");
+    CC1Args.push_back("-target-feature");
+    CC1Args.push_back("+sign-ext");
   }
 
   if (DriverArgs.getLastArg(options::OPT_fwasm_exceptions)) {
diff --git a/clang/test/Driver/wasm-toolchain.c b/clang/test/Driver/wasm-toolchain.c
--- a/clang/test/Driver/wasm-toolchain.c
+++ b/clang/test/Driver/wasm-toolchain.c
@@ -48,11 +48,11 @@
 
 // Thread-related command line tests.
 
-// '-pthread' sets +atomics, +bulk-memory, +mutable-globals, and --shared-memory
+// '-pthread' sets +atomics, +bulk-memory, +mutable-globals, +sign-ext, and --shared-memory
 // RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown \
 // RUN:    --sysroot=/foo %s -fuse-ld=wasm-ld -pthread 2>&1 \
 // RUN:  | FileCheck -check-prefix=PTHREAD %s
-// PTHREAD: clang{{.*}}" "-cc1" {{.*}} "-target-feature" "+atomics" "-target-feature" "+bulk-memory" "-target-feature" "+mutable-globals"
+// PTHREAD: clang{{.*}}" "-cc1" {{.*}} "-target-feature" "+atomics" "-target-feature" "+bulk-memory" "-target-feature" "+mutable-globals" "-target-feature" "+sign-ext"
 // PTHREAD: wasm-ld{{.*}}" "-lpthread" "--shared-memory"
 
 // '-pthread' not allowed with '-mno-atomics'
@@ -73,6 +73,12 @@
 // RUN:   | FileCheck -check-prefix=PTHREAD_NO_MUT_GLOBALS %s
 // PTHREAD_NO_MUT_GLOBALS: invalid argument '-pthread' not allowed with '-mno-mutable-globals'
 
+// '-pthread' not allowed with '-mno-sign-ext'
+// RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown \
+// RUN:     --sysroot=/foo %s -pthread -mno-sign-ext 2>&1 \
+// RUN:   | FileCheck -check-prefix=PTHREAD_NO_SIGN_EXT %s
+// PTHREAD_NO_SIGN_EXT: invalid argument '-pthread' not allowed with '-mno-sign-ext'
+
 // '-fwasm-exceptions' sets +exception-handling
 // RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown \
 // RUN:    --sysroot=/foo %s -fwasm-exceptions 2>&1 \