diff --git a/cranelift/codegen/src/isa/x64/inst.isle b/cranelift/codegen/src/isa/x64/inst.isle
index fbe4e09ac9..af1630b8e4 100644
--- a/cranelift/codegen/src/isa/x64/inst.isle
+++ b/cranelift/codegen/src/isa/x64/inst.isle
@@ -289,7 +289,8 @@
                           (src Xmm)
                           (dst WritableGpr)
                           (tmp_gpr WritableGpr)
-                          (tmp_xmm WritableXmm))
+                          (tmp_xmm WritableXmm)
+                          (tmp_xmm2 WritableXmm))
 
        ;; A sequence to compute min/max with the proper NaN semantics for xmm
        ;; registers.
@@ -3213,8 +3214,9 @@
 
             (dst WritableGpr (temp_writable_gpr))
             (tmp_xmm WritableXmm (temp_writable_xmm))
+            (tmp_xmm2 WritableXmm (temp_writable_xmm))
             (tmp_gpr WritableGpr (temp_writable_gpr))
-            (_ Unit (emit (MInst.CvtFloatToUintSeq out_size src_size is_saturating src dst tmp_gpr tmp_xmm))))
+            (_ Unit (emit (MInst.CvtFloatToUintSeq out_size src_size is_saturating src dst tmp_gpr tmp_xmm tmp_xmm2))))
         dst))
 
 (decl cvt_float_to_sint_seq (Type Value bool) Gpr)
diff --git a/cranelift/codegen/src/isa/x64/inst/emit.rs b/cranelift/codegen/src/isa/x64/inst/emit.rs
index 4a60b83c38..1a79336569 100644
--- a/cranelift/codegen/src/isa/x64/inst/emit.rs
+++ b/cranelift/codegen/src/isa/x64/inst/emit.rs
@@ -2593,11 +2593,13 @@ pub(crate) fn emit(
             dst,
             tmp_gpr,
             tmp_xmm,
+            tmp_xmm2,
         } => {
             let src = allocs.next(src.to_reg());
             let dst = allocs.next(dst.to_reg().to_reg());
             let tmp_gpr = allocs.next(tmp_gpr.to_reg().to_reg());
             let tmp_xmm = allocs.next(tmp_xmm.to_reg().to_reg());
+            let tmp_xmm2 = allocs.next(tmp_xmm2.to_reg().to_reg());
 
             // The only difference in behavior between saturating and non-saturating is how we
             // handle errors. Emits the following sequence:
@@ -2620,7 +2622,8 @@ pub(crate) fn emit(
             // -- saturating: xor %dst, %dst; j done
             //
             // is_large:
-            // subss/subsd %tmp_xmm, %src ; <-- we clobber %src here
+            // mov %src, %tmp_xmm2
+            // subss/subsd %tmp_xmm, %tmp_xmm2
             // cvttss2si/cvttss2sd %tmp_x, %dst
             // cmp 0, %dst
             // jnl next_is_large
@@ -2732,10 +2735,13 @@ pub(crate) fn emit(
 
             sink.bind_label(handle_large);
 
-            let inst = Inst::xmm_rm_r(sub_op, RegMem::reg(tmp_xmm), Writable::from_reg(src));
+            let inst = Inst::gen_move(Writable::from_reg(tmp_xmm2), src, types::F64);
             inst.emit(&[], sink, info, state);
 
-            let inst = Inst::xmm_to_gpr(trunc_op, src, Writable::from_reg(dst), *dst_size);
+            let inst = Inst::xmm_rm_r(sub_op, RegMem::reg(tmp_xmm), Writable::from_reg(tmp_xmm2));
+            inst.emit(&[], sink, info, state);
+
+            let inst = Inst::xmm_to_gpr(trunc_op, tmp_xmm2, Writable::from_reg(dst), *dst_size);
             inst.emit(&[], sink, info, state);
 
             let inst = Inst::cmp_rmi_r(*dst_size, RegMemImm::imm(0), dst);
diff --git a/cranelift/codegen/src/isa/x64/inst/mod.rs b/cranelift/codegen/src/isa/x64/inst/mod.rs
index fd449fe56a..5aa6a5b731 100644
--- a/cranelift/codegen/src/isa/x64/inst/mod.rs
+++ b/cranelift/codegen/src/isa/x64/inst/mod.rs
@@ -1179,14 +1179,16 @@ impl PrettyPrint for Inst {
                 dst_size,
                 tmp_gpr,
                 tmp_xmm,
+                tmp_xmm2,
                 is_saturating,
             } => {
                 let src = pretty_print_reg(src.to_reg(), src_size.to_bytes(), allocs);
                 let dst = pretty_print_reg(dst.to_reg().to_reg(), dst_size.to_bytes(), allocs);
                 let tmp_gpr = pretty_print_reg(tmp_gpr.to_reg().to_reg(), 8, allocs);
                 let tmp_xmm = pretty_print_reg(tmp_xmm.to_reg().to_reg(), 8, allocs);
+                let tmp_xmm2 = pretty_print_reg(tmp_xmm2.to_reg().to_reg(), 8, allocs);
                 format!(
-                    "{} {}, {}, {}, {}",
+                    "{} {}, {}, {}, {}, {}",
                     ljustify(format!(
                         "cvt_float{}_to_uint{}{}_seq",
                         src_size.to_bits(),
@@ -1197,6 +1199,7 @@ impl PrettyPrint for Inst {
                     dst,
                     tmp_gpr,
                     tmp_xmm,
+                    tmp_xmm2,
                 )
             }
 
@@ -1876,7 +1879,7 @@ fn x64_get_operands<F: Fn(VReg) -> VReg>(inst: &Inst, collector: &mut OperandCol
             ..
         } => {
             collector.reg_use(src.to_reg());
-            collector.reg_def(dst.to_writable_reg());
+            collector.reg_early_def(dst.to_writable_reg());
             collector.reg_early_def(tmp_gpr1.to_writable_reg());
             collector.reg_early_def(tmp_gpr2.to_writable_reg());
         }
@@ -1886,18 +1889,25 @@ fn x64_get_operands<F: Fn(VReg) -> VReg>(inst: &Inst, collector: &mut OperandCol
             tmp_xmm,
             tmp_gpr,
             ..
+        } => {
+            collector.reg_use(src.to_reg());
+            collector.reg_early_def(dst.to_writable_reg());
+            collector.reg_early_def(tmp_gpr.to_writable_reg());
+            collector.reg_early_def(tmp_xmm.to_writable_reg());
         }
-        | Inst::CvtFloatToUintSeq {
+        Inst::CvtFloatToUintSeq {
             src,
             dst,
             tmp_gpr,
             tmp_xmm,
+            tmp_xmm2,
             ..
         } => {
             collector.reg_use(src.to_reg());
-            collector.reg_def(dst.to_writable_reg());
+            collector.reg_early_def(dst.to_writable_reg());
             collector.reg_early_def(tmp_gpr.to_writable_reg());
             collector.reg_early_def(tmp_xmm.to_writable_reg());
+            collector.reg_early_def(tmp_xmm2.to_writable_reg());
         }
         Inst::MovzxRmR { src, dst, .. } => {
             collector.reg_def(dst.to_writable_reg());
diff --git a/cranelift/filetests/filetests/isa/x64/fcvt.clif b/cranelift/filetests/filetests/isa/x64/fcvt.clif
index 3429078f59..97734701f4 100644
--- a/cranelift/filetests/filetests/isa/x64/fcvt.clif
+++ b/cranelift/filetests/filetests/isa/x64/fcvt.clif
@@ -209,7 +209,7 @@ block0(v0: f32):
 ;   pushq   %rbp
 ;   movq    %rsp, %rbp
 ; block0:
-;   cvt_float32_to_uint32_seq %xmm0, %eax, %r8, %xmm4
+;   cvt_float32_to_uint32_seq %xmm0, %eax, %r9, %xmm4, %xmm5
 ;   movq    %rbp, %rsp
 ;   popq    %rbp
 ;   ret
@@ -223,7 +223,7 @@ block0(v0: f32):
 ;   pushq   %rbp
 ;   movq    %rsp, %rbp
 ; block0:
-;   cvt_float32_to_uint64_seq %xmm0, %rax, %r8, %xmm4
+;   cvt_float32_to_uint64_seq %xmm0, %rax, %r9, %xmm4, %xmm5
 ;   movq    %rbp, %rsp
 ;   popq    %rbp
 ;   ret
@@ -237,7 +237,7 @@ block0(v0: f64):
 ;   pushq   %rbp
 ;   movq    %rsp, %rbp
 ; block0:
-;   cvt_float64_to_uint32_seq %xmm0, %eax, %r8, %xmm4
+;   cvt_float64_to_uint32_seq %xmm0, %eax, %r9, %xmm4, %xmm5
 ;   movq    %rbp, %rsp
 ;   popq    %rbp
 ;   ret
@@ -251,7 +251,7 @@ block0(v0: f64):
 ;   pushq   %rbp
 ;   movq    %rsp, %rbp
 ; block0:
-;   cvt_float64_to_uint64_seq %xmm0, %rax, %r8, %xmm4
+;   cvt_float64_to_uint64_seq %xmm0, %rax, %r9, %xmm4, %xmm5
 ;   movq    %rbp, %rsp
 ;   popq    %rbp
 ;   ret
@@ -265,7 +265,7 @@ block0(v0: f32):
 ;   pushq   %rbp
 ;   movq    %rsp, %rbp
 ; block0:
-;   cvt_float32_to_uint32_sat_seq %xmm0, %eax, %r8, %xmm4
+;   cvt_float32_to_uint32_sat_seq %xmm0, %eax, %r9, %xmm4, %xmm5
 ;   movq    %rbp, %rsp
 ;   popq    %rbp
 ;   ret
@@ -279,7 +279,7 @@ block0(v0: f32):
 ;   pushq   %rbp
 ;   movq    %rsp, %rbp
 ; block0:
-;   cvt_float32_to_uint64_sat_seq %xmm0, %rax, %r8, %xmm4
+;   cvt_float32_to_uint64_sat_seq %xmm0, %rax, %r9, %xmm4, %xmm5
 ;   movq    %rbp, %rsp
 ;   popq    %rbp
 ;   ret
@@ -293,7 +293,7 @@ block0(v0: f64):
 ;   pushq   %rbp
 ;   movq    %rsp, %rbp
 ; block0:
-;   cvt_float64_to_uint32_sat_seq %xmm0, %eax, %r8, %xmm4
+;   cvt_float64_to_uint32_sat_seq %xmm0, %eax, %r9, %xmm4, %xmm5
 ;   movq    %rbp, %rsp
 ;   popq    %rbp
 ;   ret
@@ -307,7 +307,7 @@ block0(v0: f64):
 ;   pushq   %rbp
 ;   movq    %rsp, %rbp
 ; block0:
-;   cvt_float64_to_uint64_sat_seq %xmm0, %rax, %r8, %xmm4
+;   cvt_float64_to_uint64_sat_seq %xmm0, %rax, %r9, %xmm4, %xmm5
 ;   movq    %rbp, %rsp
 ;   popq    %rbp
 ;   ret
diff --git a/tests/misc_testsuite/issue4840.wast b/tests/misc_testsuite/issue4840.wast
new file mode 100644
index 0000000000..406b8cb6cd
--- /dev/null
+++ b/tests/misc_testsuite/issue4840.wast
@@ -0,0 +1,16 @@
+(module
+  (func (export "f") (param f32 i32) (result f64)
+    local.get 1
+    f64.convert_i32_u
+    i32.trunc_f64_u
+    f64.convert_i32_s
+    local.get 1
+    f64.convert_i32_u
+    global.set 0
+    drop
+    global.get 0
+  )
+  (global (;0;) (mut f64) f64.const 0)
+)
+
+(assert_return (invoke "f" (f32.const 1.23) (i32.const -2147483648)) (f64.const 2147483648))