Index: llvm/lib/InterfaceStub/IFSHandler.cpp
===================================================================
--- llvm/lib/InterfaceStub/IFSHandler.cpp
+++ llvm/lib/InterfaceStub/IFSHandler.cpp
@@ -193,8 +193,14 @@
         "IFS version " + Stub->IfsVersion.getAsString() + " is unsupported.",
         std::make_error_code(std::errc::invalid_argument));
   if (Stub->Target.ArchString) {
-    Stub->Target.Arch =
+    uint16_t eMachine =
         ELF::convertArchNameToEMachine(*Stub->Target.ArchString);
+    if (eMachine == ELF::EM_NONE) {
+      return make_error<StringError>(
+          "IFS Arch '" + *Stub->Target.ArchString + "' is unsupported.",
+          std::make_error_code(std::errc::invalid_argument));
+    }
+    Stub->Target.Arch = eMachine;
   }
   return std::move(Stub);
 }
Index: llvm/test/tools/llvm-ifs/ifs-read-invalid-arch.test
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-ifs/ifs-read-invalid-arch.test
@@ -0,0 +1,15 @@
+# RUN: not llvm-ifs --output-ifs=- %s 2>&1 | FileCheck %s
+
+--- !ifs-v1
+SoName: somelib.so
+IfsVersion: 3.0
+Target: { ObjectFormat: ELF, Arch: RiscV64, Endianness: little, BitWidth: 64 }
+Symbols:
+  - { Name: foo, Type: Func }
+  - { Name: bar, Type: Object, Size: 42 }
+  - { Name: baz, Type: Object, Size: 8 }
+  - { Name: not, Type: Object, Size: 128, Undefined: true }
+  - { Name: nor, Type: Func, Undefined: true }
+...
+
+# CHECK: error: IFS Arch 'RiscV64' is unsupported.
Index: llvm/test/tools/llvm-ifs/write-stub.test
===================================================================
--- llvm/test/tools/llvm-ifs/write-stub.test
+++ llvm/test/tools/llvm-ifs/write-stub.test
@@ -38,6 +38,8 @@
 
 # RUN: llvm-ifs --output-elf=- --target=riscv64-linux-gnu %s | llvm-readelf -h - | FileCheck %s --check-prefix=MACHINE
 
+# RUN: not llvm-ifs --output-elf=- --arch=riscv64 --endianness=little --bitwidth=64 %s 2>&1 | FileCheck %s -DMSG=riscv64 --check-prefix=ARCHERR
+
 --- !ifs-v1
 IfsVersion: 3.0
 NeededLibs:
@@ -207,3 +209,5 @@
 # CONFLICTERR: error: Supplied [[MSG]] conflicts with the text stub
 
 # MACHINE: Machine: RISC-V
+
+# ARCHERR: error: Unknown arch '[[MSG]]'!
Index: llvm/tools/llvm-ifs/llvm-ifs.cpp
===================================================================
--- llvm/tools/llvm-ifs/llvm-ifs.cpp
+++ llvm/tools/llvm-ifs/llvm-ifs.cpp
@@ -333,9 +333,13 @@
     if (!Config.OutputFormat)
       OptionNotFound("--output-format", A->getValue());
   }
-  if (const opt::Arg *A = Args.getLastArg(OPT_arch_EQ))
-    Config.OverrideArch = ELF::convertArchNameToEMachine(A->getValue());
-
+  if (const opt::Arg *A = Args.getLastArg(OPT_arch_EQ)) {
+    uint16_t eMachine = ELF::convertArchNameToEMachine(A->getValue());
+    if (eMachine == ELF::EM_NONE) {
+      fatalError(Twine("Unknown arch '") + A->getValue() + "'!");
+    }
+    Config.OverrideArch = eMachine;
+  }
   if (const opt::Arg *A = Args.getLastArg(OPT_bitwidth_EQ)) {
     size_t Width;
     llvm::StringRef S(A->getValue());