diff --git a/llvm/lib/Support/RISCVISAInfo.cpp b/llvm/lib/Support/RISCVISAInfo.cpp
index 2ad5a3cd5a56..994fba36b13c 100644
--- a/llvm/lib/Support/RISCVISAInfo.cpp
+++ b/llvm/lib/Support/RISCVISAInfo.cpp
@@ -1101,6 +1101,8 @@ std::vector<std::string> RISCVISAInfo::toFeatureVector() const {
     std::string ExtName = Ext.first;
     if (ExtName == "i") // i is not recognized in clang -cc1
       continue;
+    if (!isSupportedExtension(ExtName))
+      continue;
     std::string Feature = isExperimentalExtension(ExtName)
                               ? "+experimental-" + ExtName
                               : "+" + ExtName;
diff --git a/llvm/unittests/Support/RISCVISAInfoTest.cpp b/llvm/unittests/Support/RISCVISAInfoTest.cpp
index 05997d2d2d2c..27b00709f2bb 100644
--- a/llvm/unittests/Support/RISCVISAInfoTest.cpp
+++ b/llvm/unittests/Support/RISCVISAInfoTest.cpp
@@ -446,3 +446,10 @@ TEST(ToFeatureVector, IIsDroppedAndExperimentalExtensionsArePrefixed) {
   EXPECT_THAT((*MaybeISAInfo2)->toFeatureVector(),
               ElementsAre("+e", "+experimental-zihintntl", "+xventanacondops"));
 }
+
+TEST(ToFeatureVector, UnsupportedExtensionsAreDropped) {
+  auto MaybeISAInfo =
+      RISCVISAInfo::parseNormalizedArchString("rv64i2p0_m2p0_xmadeup1p0");
+  ASSERT_THAT_EXPECTED(MaybeISAInfo, Succeeded());
+  EXPECT_THAT((*MaybeISAInfo)->toFeatureVector(), ElementsAre("+m"));
+}