diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5467,6 +5467,15 @@
   if (!In->isNaN())
     return ConstantFP::getNaN(Ty);
 
+  // If we known this is a NaN, and it's scalable vector, we must have a splat
+  // on our hands. Grab that before splatting a QNaN constant.
+  if (isa<ScalableVectorType>(Ty)) {
+    auto *Splat = In->getSplatValue();
+    assert(Splat && Splat->isNaN() &&
+           "Found a scalable-vector NaN but not a splat");
+    In = Splat;
+  }
+
   // Propagate an existing QNaN constant. If it is an SNaN, make it quiet, but
   // preserve the sign/payload.
   return ConstantFP::get(Ty, cast<ConstantFP>(In)->getValue().makeQuiet());
diff --git a/llvm/test/Transforms/InstSimplify/fp-nan.ll b/llvm/test/Transforms/InstSimplify/fp-nan.ll
--- a/llvm/test/Transforms/InstSimplify/fp-nan.ll
+++ b/llvm/test/Transforms/InstSimplify/fp-nan.ll
@@ -49,6 +49,14 @@
   ret <2 x float> %r
 }
 
+define <vscale x 1 x float> @fsub_nan_op1_scalable_vec(<vscale x 1 x float> %x) {
+; CHECK-LABEL: @fsub_nan_op1_scalable_vec(
+; CHECK-NEXT:    ret <vscale x 1 x float> shufflevector (<vscale x 1 x float> insertelement (<vscale x 1 x float> poison, float 0x7FF9000000000000, i64 0), <vscale x 1 x float> poison, <vscale x 1 x i32> zeroinitializer)
+;
+  %r = fsub <vscale x 1 x float> %x, shufflevector (<vscale x 1 x float> insertelement (<vscale x 1 x float> poison, float 0x7FF1000000000000, i64 0), <vscale x 1 x float> poison, <vscale x 1 x i32> zeroinitializer)
+  ret <vscale x 1 x float> %r
+}
+
 ; Signaling and signed - make quiet and preserve the payload and signbit
 
 define double @fmul_nan_op0(double %x) {