diff --git a/runtime/stack.cc b/runtime/stack.cc
index a765a3f..d956f0e 100644
--- a/runtime/stack.cc
+++ b/runtime/stack.cc
@@ -325,6 +325,10 @@
 
 bool StackVisitor::GetRegisterIfAccessible(uint32_t reg, VRegKind kind, uint32_t* val) const {
   const bool is_float = (kind == kFloatVReg) || (kind == kDoubleLoVReg) || (kind == kDoubleHiVReg);
+
+  // X86 float registers are 64-bit and the logic below does not apply.
+  DCHECK(!is_float || kRuntimeISA != InstructionSet::kX86);
+
   if (!IsAccessibleRegister(reg, is_float)) {
     return false;
   }