diff --git a/clang/include/clang/Basic/DiagnosticDriverKinds.td b/clang/include/clang/Basic/DiagnosticDriverKinds.td
--- a/clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ b/clang/include/clang/Basic/DiagnosticDriverKinds.td
@@ -682,4 +682,7 @@
 def warn_drv_sarif_format_unstable : Warning<
   "diagnostic formatting in SARIF mode is currently unstable">,
   InGroup<DiagGroup<"sarif-format-unstable">>;
+
+def err_drv_riscv_unsupported_with_linker_relaxation : Error<
+  "%0 is unsupported with RISC-V linker relaxation (-mrelax)">;
 }
diff --git a/clang/lib/Driver/ToolChains/Arch/RISCV.cpp b/clang/lib/Driver/ToolChains/Arch/RISCV.cpp
--- a/clang/lib/Driver/ToolChains/Arch/RISCV.cpp
+++ b/clang/lib/Driver/ToolChains/Arch/RISCV.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "RISCV.h"
+#include "../Clang.h"
 #include "ToolChains/CommonArgs.h"
 #include "clang/Basic/CharInfo.h"
 #include "clang/Driver/Driver.h"
@@ -137,10 +138,17 @@
     Features.push_back("+reserve-x31");
 
   // -mrelax is default, unless -mno-relax is specified.
-  if (Args.hasFlag(options::OPT_mrelax, options::OPT_mno_relax, true))
+  if (Args.hasFlag(options::OPT_mrelax, options::OPT_mno_relax, true)) {
     Features.push_back("+relax");
-  else
+    // -gsplit-dwarf -mrelax requires DW_AT_high_pc/DW_AT_ranges/... indexing
+    // into .debug_addr, which is currently not implemented.
+    Arg *A;
+    if (getDebugFissionKind(D, Args, A) != DwarfFissionKind::None)
+      D.Diag(clang::diag::err_drv_riscv_unsupported_with_linker_relaxation)
+          << A->getAsString(Args);
+  } else {
     Features.push_back("-relax");
+  }
 
   // GCC Compatibility: -mno-save-restore is default, unless -msave-restore is
   // specified.
diff --git a/clang/lib/Driver/ToolChains/Clang.h b/clang/lib/Driver/ToolChains/Clang.h
--- a/clang/lib/Driver/ToolChains/Clang.h
+++ b/clang/lib/Driver/ToolChains/Clang.h
@@ -198,6 +198,12 @@
                     const char *LinkingOutput) const override;
 };
 
+enum class DwarfFissionKind { None, Split, Single };
+
+DwarfFissionKind getDebugFissionKind(const Driver &D,
+                                     const llvm::opt::ArgList &Args,
+                                     llvm::opt::Arg *&Arg);
+
 } // end namespace tools
 
 } // end namespace driver
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -4034,9 +4034,7 @@
                      options::OPT_fno_spell_checking);
 }
 
-enum class DwarfFissionKind { None, Split, Single };
-
-static DwarfFissionKind getDebugFissionKind(const Driver &D,
+DwarfFissionKind tools::getDebugFissionKind(const Driver &D,
                                             const ArgList &Args, Arg *&Arg) {
   Arg = Args.getLastArg(options::OPT_gsplit_dwarf, options::OPT_gsplit_dwarf_EQ,
                         options::OPT_gno_split_dwarf);
diff --git a/clang/test/Driver/riscv-features.c b/clang/test/Driver/riscv-features.c
--- a/clang/test/Driver/riscv-features.c
+++ b/clang/test/Driver/riscv-features.c
@@ -35,3 +35,10 @@
 // RUN: not %clang -cc1 -triple riscv64-unknown-elf -target-feature +e 2>&1 | FileCheck %s -check-prefix=RV64-WITH-E
 
 // RV64-WITH-E: error: invalid feature combination: standard user-level extension 'e' requires 'rv32'
+
+// RUN: not %clang -c --target=riscv64-linux-gnu -gsplit-dwarf %s 2>&1 | FileCheck %s --check-prefix=ERR-SPLIT-DWARF
+// RUN: not %clang -c --target=riscv64 -gsplit-dwarf=single %s 2>&1 | FileCheck %s --check-prefix=ERR-SPLIT-DWARF
+// RUN: %clang -### -c --target=riscv64 -mno-relax -g -gsplit-dwarf %s 2>&1 | FileCheck %s --check-prefix=SPLIT-DWARF
+
+// ERR-SPLIT-DWARF: error: -gsplit-dwarf{{.*}} is unsupported with RISC-V linker relaxation (-mrelax)
+// SPLIT-DWARF:     "-split-dwarf-file"