diff --git a/llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp b/llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
--- a/llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
+++ b/llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
@@ -3299,6 +3299,7 @@
     {"pauth", {AArch64::FeaturePAuth}},
     {"flagm", {AArch64::FeatureFlagM}},
     {"rme", {AArch64::FeatureRME}},
+    {"sme", {AArch64::FeatureSME}},
     // FIXME: Unsupported extensions
     {"lor", {}},
     {"rdma", {}},
diff --git a/llvm/test/MC/AArch64/SME/directives-negative.s b/llvm/test/MC/AArch64/SME/directives-negative.s
new file mode 100644
--- /dev/null
+++ b/llvm/test/MC/AArch64/SME/directives-negative.s
@@ -0,0 +1,14 @@
+// RUN: not llvm-mc -triple=aarch64 < %s
+
+.arch_extension sme
+.arch_extension nosme
+
+smstart
+// CHECK: error: instruction requires: sme
+// CHECK-NEXT: smstart
+
+.arch armv8-a+sme
+.arch armv8-a+nosme
+smstart
+// CHECK: error: instruction requires: sme
+// CHECK-NEXT: smstart
diff --git a/llvm/test/MC/AArch64/SME/directives.s b/llvm/test/MC/AArch64/SME/directives.s
new file mode 100644
--- /dev/null
+++ b/llvm/test/MC/AArch64/SME/directives.s
@@ -0,0 +1,12 @@
+// RUN: llvm-mc -triple=aarch64 < %s | FileCheck %s
+
+.arch_extension sme
+
+smstart
+// CHECK: smstart
+
+.arch_extension nosme
+
+.arch armv8-a+sme
+smstart
+// CHECK: smstart