diff --git a/src/hotspot/cpu/riscv/gc/g1/g1BarrierSetAssembler_riscv.cpp b/src/hotspot/cpu/riscv/gc/g1/g1BarrierSetAssembler_riscv.cpp
index 72b69d16943..9c3bd93f8a6 100644
--- a/src/hotspot/cpu/riscv/gc/g1/g1BarrierSetAssembler_riscv.cpp
+++ b/src/hotspot/cpu/riscv/gc/g1/g1BarrierSetAssembler_riscv.cpp
@@ -87,21 +87,31 @@ void G1BarrierSetAssembler::gen_write_ref_array_pre_barrier(MacroAssembler* masm
   }
 }
 
-void G1BarrierSetAssembler::gen_write_ref_array_post_barrier(MacroAssembler* masm, DecoratorSet decorators,
-                                                             Register start, Register count, Register tmp, RegSet saved_regs) {
+void G1BarrierSetAssembler::gen_write_ref_array_post_barrier(MacroAssembler* masm,
+                                                             DecoratorSet decorators,
+                                                             Register start,
+                                                             Register count,
+                                                             Register tmp,
+                                                             RegSet saved_regs) {
+  assert_different_registers(start, count, tmp);
+
   Label loop, next, done;
-  const Register end = count;
 
   // Zero count? Nothing to do.
   __ beqz(count, done);
 
-  __ shadd(end, count, start, tmp, LogBytesPerHeapOop); // end = start + count << LogBytesPerHeapOop
-  __ subi(end, end, BytesPerHeapOop);                   // last element address to make inclusive
+  // Calculate the number of card marks to set. Since the object might start and
+  // end within a card, we need to calculate this via the card table indexes of
+  // the actual start and last addresses covered by the object.
+  // Temporarily use the count register for the last element address.
+  __ shadd(count, count, start, tmp, LogBytesPerHeapOop); // end = start + count << LogBytesPerHeapOop
+  __ subi(count, count, BytesPerHeapOop);                 // Use last element address for end.
 
   __ srli(start, start, CardTable::card_shift());
-  __ srli(end, end, CardTable::card_shift());
-  __ sub(count, end, start);                            // Number of bytes to mark - 1
+  __ srli(count, count, CardTable::card_shift());
+  __ sub(count, count, start);                            // Number of bytes to mark - 1.
 
+  // Add card table base offset to start.
   Address card_table_address(xthread, G1ThreadLocalData::card_table_base_offset());
   __ ld(tmp, card_table_address);
   __ add(start, start, tmp);
@@ -109,14 +119,15 @@ void G1BarrierSetAssembler::gen_write_ref_array_post_barrier(MacroAssembler* mas
   __ bind(loop);
   if (UseCondCardMark) {
     __ add(tmp, start, count);
-    static_assert((uint)G1CardTable::clean_card_val() == 0xff, "must be");
     __ lbu(tmp, Address(tmp, 0));
-    __ subi(tmp, tmp, G1CardTable::clean_card_val());   // Convert to clean_card_value() to a comparison
-                                                        // against zero to avoid use of an extra temp.
+    static_assert((uint)G1CardTable::clean_card_val() == 0xff, "must be");
+    __ subi(tmp, tmp, G1CardTable::clean_card_val()); // Convert to clean_card_value() to a comparison
+                                                      // against zero to avoid use of an extra temp.
     __ bnez(tmp, next);
   }
-  static_assert(G1CardTable::dirty_card_val() == 0, "must be to use zr");
+
   __ add(tmp, start, count);
+  static_assert(G1CardTable::dirty_card_val() == 0, "must be to use zr");
   __ sb(zr, Address(tmp, 0));
 
   __ bind(next);