diff --git a/src/dynarmic/backend/x64/a32_emit_x64_memory.cpp b/src/dynarmic/backend/x64/a32_emit_x64_memory.cpp
index 33f1ddfc..82e9ae96 100644
--- a/src/dynarmic/backend/x64/a32_emit_x64_memory.cpp
+++ b/src/dynarmic/backend/x64/a32_emit_x64_memory.cpp
@@ -85,6 +85,7 @@ void A32EmitX64::GenFastmemFallbacks() {
                         code.mov(code.ABI_PARAM2, Xbyak::Reg64{vaddr_idx});
                     }
                 }
+                code.ZeroExtendFrom(bitsize, code.ABI_PARAM3);
                 callback.EmitCall(code);
                 ABI_PopCallerSaveRegistersAndAdjustStack(code);
                 code.ret();
@@ -110,7 +111,9 @@ void A32EmitX64::GenFastmemFallbacks() {
                         code.mov(code.ABI_PARAM2, Xbyak::Reg64{vaddr_idx});
                     }
                 }
+                code.ZeroExtendFrom(bitsize, code.ABI_PARAM3);
                 code.mov(code.ABI_PARAM4, rax);
+                code.ZeroExtendFrom(bitsize, code.ABI_PARAM4);
                 callback.EmitCall(code);
                 ABI_PopCallerSaveRegistersAndAdjustStackExcept(code, HostLoc::RAX);
                 code.ret();
diff --git a/src/dynarmic/backend/x64/a64_emit_x64_memory.cpp b/src/dynarmic/backend/x64/a64_emit_x64_memory.cpp
index 2c0e50a5..14cb665e 100644
--- a/src/dynarmic/backend/x64/a64_emit_x64_memory.cpp
+++ b/src/dynarmic/backend/x64/a64_emit_x64_memory.cpp
@@ -227,6 +227,7 @@ void A64EmitX64::GenFastmemFallbacks() {
                         code.mov(code.ABI_PARAM2, Xbyak::Reg64{vaddr_idx});
                     }
                 }
+                code.ZeroExtendFrom(bitsize, code.ABI_PARAM3);
                 callback.EmitCall(code);
                 ABI_PopCallerSaveRegistersAndAdjustStack(code);
                 code.ret();
@@ -252,7 +253,9 @@ void A64EmitX64::GenFastmemFallbacks() {
                         code.mov(code.ABI_PARAM2, Xbyak::Reg64{vaddr_idx});
                     }
                 }
+                code.ZeroExtendFrom(bitsize, code.ABI_PARAM3);
                 code.mov(code.ABI_PARAM4, rax);
+                code.ZeroExtendFrom(bitsize, code.ABI_PARAM4);
                 callback.EmitCall(code);
                 ABI_PopCallerSaveRegistersAndAdjustStackExcept(code, HostLoc::RAX);
                 code.ret();