diff --git a/include/isa/riscv64.h b/include/isa/riscv64.h
index eb95f00231a69ba71e75ad8108a2ef2789148d87..4c11ce0052045edcbfc589079ae30d372d059fd5 100644
--- a/include/isa/riscv64.h
+++ b/include/isa/riscv64.h
@@ -18,6 +18,10 @@ typedef struct {
     uint64_t _64;
   } gpr[32];
 
+  union {
+    uint64_t _64;
+  } fpr[32];
+
   uint64_t pc;
   uint64_t mstatus, mcause, mepc;
   uint64_t sstatus, scause, sepc;
diff --git a/src/isa/riscv64/difftest/difftest.h b/src/isa/riscv64/difftest/difftest.h
index 7218cab8065331058ba24025ea2d2acaa177d65e..6c78cae058b417277dd54feba4f4a28fa41d5202 100644
--- a/src/isa/riscv64/difftest/difftest.h
+++ b/src/isa/riscv64/difftest/difftest.h
@@ -1,7 +1,7 @@
 #ifndef __RISCV64_DIFF_TEST_H__
 #define __RISCV64_DIFF_TEST_H__
 
-#define DIFFTEST_REG_SIZE (sizeof(uint64_t) * (32 + 1 + 6)) // GRPs + pc + [m|s][status|cause|epc]
+#define DIFFTEST_REG_SIZE (sizeof(uint64_t) * (32 + 32 + 1 + 6)) // GRPs + FPRs + pc + [m|s][status|cause|epc]
 
 void isa_difftest_getregs_hook(void);
 void isa_difftest_setregs_hook(void);
diff --git a/tools/qemu-diff/include/isa/riscv64.h b/tools/qemu-diff/include/isa/riscv64.h
index 2ddd38c40198a676b75c6f5af2a750276f81dd9d..850a2ae69f64f6353a007cf9f61865b040703ed2 100644
--- a/tools/qemu-diff/include/isa/riscv64.h
+++ b/tools/qemu-diff/include/isa/riscv64.h
@@ -9,10 +9,11 @@
 union isa_gdb_regs {
   struct {
     uint64_t gpr[32];
+    uint64_t fpr[32];
     uint64_t pc;
   };
   struct {
-    uint32_t array[77];
+    uint32_t array[DIFFTEST_REG_SIZE/sizeof(uint32_t)];
   };
 };