diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -533,6 +533,10 @@
       setOperationAction(ISD::SPLAT_VECTOR, VT, Legal);
       setOperationAction(ISD::SPLAT_VECTOR_PARTS, VT, Custom);
 
+      // Vectors implement MULHS/MULHU.
+      setOperationAction(ISD::SMUL_LOHI, VT, Expand);
+      setOperationAction(ISD::UMUL_LOHI, VT, Expand);
+
       setOperationAction(ISD::SMIN, VT, Legal);
       setOperationAction(ISD::SMAX, VT, Legal);
       setOperationAction(ISD::UMIN, VT, Legal);