diff --git a/src/cmd/compile/internal/mips64/ssa.go b/src/cmd/compile/internal/mips64/ssa.go
index 2727c4d8a8..b0e0165ad8 100644
--- a/src/cmd/compile/internal/mips64/ssa.go
+++ b/src/cmd/compile/internal/mips64/ssa.go
@@ -321,7 +321,10 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		for a.Op == ssa.OpCopy || a.Op == ssa.OpMIPS64MOVVreg {
 			a = a.Args[0]
 		}
-		if a.Op == ssa.OpLoadReg {
+		if a.Op == ssa.OpLoadReg && mips.REG_R0 <= a.Reg() && a.Reg() <= mips.REG_R31 {
+			// LoadReg from a narrower type does an extension, except loading
+			// to a floating point register. So only eliminate the extension
+			// if it is loaded to an integer register.
 			t := a.Type
 			switch {
 			case v.Op == ssa.OpMIPS64MOVBreg && t.Size() == 1 && t.IsSigned(),
diff --git a/test/fixedbugs/issue50671.go b/test/fixedbugs/issue50671.go
new file mode 100644
index 0000000000..9f4742bfcd
--- /dev/null
+++ b/test/fixedbugs/issue50671.go
@@ -0,0 +1,35 @@
+// run
+
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 50671: sign extension eliminated incorrectly on MIPS64.
+
+package main
+
+//go:noinline
+func F(x int32) (float64, int64) {
+	a := float64(x)
+	b := int64(x)
+	return a, b
+}
+
+var a, b, c float64
+
+// Poison some floating point registers with non-zero high bits.
+//
+//go:noinline
+func poison(x float64) {
+	a = x - 123.45
+	b = a * 1.2
+	c = b + 3.4
+}
+
+func main() {
+	poison(333.3)
+	_, b := F(123)
+	if b != 123 {
+		panic("FAIL")
+	}
+}