diff --git a/clang/test/Driver/riscv-arch.c b/clang/test/Driver/riscv-arch.c
--- a/clang/test/Driver/riscv-arch.c
+++ b/clang/test/Driver/riscv-arch.c
@@ -541,3 +541,14 @@
 // RUN: -fsyntax-only 2>&1 | FileCheck -check-prefix=RV32-D-ZDINX-ER %s
 // RV32-D-ZDINX-ER: error: invalid arch name 'rv32idzdinx',
 // RV32-D-ZFINX-ER: 'f' and 'zfinx' extensions are incompatible
+
+// RUN: %clang --target=riscv32-unknown-elf -march=rv32ef -### %s \
+// RUN: -fsyntax-only 2>&1 | FileCheck -check-prefix=RV32-EF-BADVARS %s
+// RV32-EF-BADVARS: error: invalid arch name 'rv32ef',
+// RV32-EF-BADVARS: 'e' extension is incompatible with 'f' extension
+
+// RUN: %clang --target=riscv32-unknown-elf -march=rv32ed -### %s \
+// RUN: -fsyntax-only 2>&1 | FileCheck -check-prefix=RV32-ED-BADVARS %s
+// RV32-ED-BADVARS: error: invalid arch name 'rv32ed',
+// RV32-ED-BADVARS: 'e' extension is incompatible with 'f' extension and 'd' extension
+
diff --git a/llvm/lib/Support/RISCVISAInfo.cpp b/llvm/lib/Support/RISCVISAInfo.cpp
--- a/llvm/lib/Support/RISCVISAInfo.cpp
+++ b/llvm/lib/Support/RISCVISAInfo.cpp
@@ -895,6 +895,7 @@
 Error RISCVISAInfo::checkDependency() {
   bool HasC = Exts.count("c") != 0;
   bool HasF = Exts.count("f") != 0;
+  bool HasD = Exts.count("d") != 0;
   bool HasZfinx = Exts.count("zfinx") != 0;
   bool HasVector = Exts.count("zve32x") != 0;
   bool HasZvl = MinVLen != 0;
@@ -931,7 +932,7 @@
         errc::invalid_argument,
         "'zvknhb' requires 'v' or 'zve64*' extension to also be specified");
 
-  if ((HasZcmt || Exts.count("zcmp")) && Exts.count("d") &&
+  if ((HasZcmt || Exts.count("zcmp")) && HasD &&
       (HasC || Exts.count("zcd")))
     return createStringError(
         errc::invalid_argument,
@@ -944,8 +945,17 @@
                              "'zcf' is only supported for 'rv32'");
 
   // Additional dependency checks.
-  // TODO: The 'q' extension requires rv64.
-  // TODO: It is illegal to specify 'e' extensions with 'f' and 'd'.
+  // The 'q' extension requires rv64.
+  if (XLen != 64 && Exts.count("q"))
+    return createStringError(errc::invalid_argument,
+                             "'q' extension is only supported for 'rv64'");
+
+  // It is illegal to specify 'e' extensions with 'f' and 'd'.
+  if (Exts.count("e") && (HasF || HasD))
+    return createStringError(
+        errc::invalid_argument,
+        Twine("'e' extension is incompatible with ") +
+            (HasD ? "'f' extension and 'd' extension" : "'f' extension"));
 
   return Error::success();
 }
diff --git a/llvm/unittests/Support/RISCVISAInfoTest.cpp b/llvm/unittests/Support/RISCVISAInfoTest.cpp
--- a/llvm/unittests/Support/RISCVISAInfoTest.cpp
+++ b/llvm/unittests/Support/RISCVISAInfoTest.cpp
@@ -474,6 +474,17 @@
     EXPECT_EQ(toString(RISCVISAInfo::parseArchString(Input, true).takeError()),
               "'zcf' is only supported for 'rv32'");
   }
+
+  for (StringRef Input : {"rv64efd", "rv32efd", "rv64ed", "rv32ed"}) {
+    EXPECT_EQ(toString(RISCVISAInfo::parseArchString(Input, true).takeError()),
+              "'e' extension is incompatible with 'f' extension"
+              " and 'd' extension");
+  }
+
+  for (StringRef Input : {"rv64ef", "rv32ef"}) {
+    EXPECT_EQ(toString(RISCVISAInfo::parseArchString(Input, true).takeError()),
+              "'e' extension is incompatible with 'f' extension");
+  }
 }
 
 TEST(ToFeatureVector, IIsDroppedAndExperimentalExtensionsArePrefixed) {