diff --git a/src/developer/debug/zxdb/client/frame_symbol_data_provider.cc b/src/developer/debug/zxdb/client/frame_symbol_data_provider.cc
index 45c9c07..ac1087e 100644
--- a/src/developer/debug/zxdb/client/frame_symbol_data_provider.cc
+++ b/src/developer/debug/zxdb/client/frame_symbol_data_provider.cc
@@ -36,24 +36,27 @@
   frame_ = nullptr;
 }
 
-std::optional<uint64_t> FrameSymbolDataProvider::GetRegister(
-    debug_ipc::RegisterID id) {
+bool FrameSymbolDataProvider::GetRegister(debug_ipc::RegisterID id,
+                                          std::optional<uint64_t>* value) {
+  *value = std::nullopt;
   if (!frame_)
-    return std::nullopt;
+    return true;  // Synchronously know we don't have the value.
 
   // Some common registers are known without having to do a register request.
   switch (debug_ipc::GetSpecialRegisterType(id)) {
     case debug_ipc::SpecialRegisterType::kIP:
-      return frame_->GetAddress();
+      *value = frame_->GetAddress();
+      return true;
     case debug_ipc::SpecialRegisterType::kSP:
-      return frame_->GetStackPointer();
+      *value = frame_->GetStackPointer();
+      return true;
     case debug_ipc::SpecialRegisterType::kNone:
       break;
   }
 
   // TODO(brettw) enable synchronous access if the registers are cached.
   // See GetRegisterAsync().
-  return std::nullopt;
+  return false;
 }
 
 void FrameSymbolDataProvider::GetRegisterAsync(debug_ipc::RegisterID id,
diff --git a/src/developer/debug/zxdb/client/frame_symbol_data_provider.h b/src/developer/debug/zxdb/client/frame_symbol_data_provider.h
index 5b3028a..6168193 100644
--- a/src/developer/debug/zxdb/client/frame_symbol_data_provider.h
+++ b/src/developer/debug/zxdb/client/frame_symbol_data_provider.h
@@ -2,7 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#pragma once
+#ifndef SRC_DEVELOPER_DEBUG_ZXDB_CLIENT_FRAME_SYMBOL_DATA_PROVIDER_H_
+#define SRC_DEVELOPER_DEBUG_ZXDB_CLIENT_FRAME_SYMBOL_DATA_PROVIDER_H_
 
 #include "src/developer/debug/zxdb/client/process_symbol_data_provider.h"
 
@@ -19,7 +20,8 @@
   void Disown() override;
 
   // SymbolDataProvider implementation:
-  std::optional<uint64_t> GetRegister(debug_ipc::RegisterID id) override;
+  bool GetRegister(debug_ipc::RegisterID id,
+                   std::optional<uint64_t>* value) override;
   void GetRegisterAsync(debug_ipc::RegisterID id,
                         GetRegisterCallback callback) override;
   std::optional<uint64_t> GetFrameBase() override;
@@ -42,3 +44,5 @@
 };
 
 }  // namespace zxdb
+
+#endif  // SRC_DEVELOPER_DEBUG_ZXDB_CLIENT_FRAME_SYMBOL_DATA_PROVIDER_H_
diff --git a/src/developer/debug/zxdb/expr/symbol_eval_context_unittest.cc b/src/developer/debug/zxdb/expr/symbol_eval_context_unittest.cc
index 2914e80..deadb6c 100644
--- a/src/developer/debug/zxdb/expr/symbol_eval_context_unittest.cc
+++ b/src/developer/debug/zxdb/expr/symbol_eval_context_unittest.cc
@@ -178,10 +178,7 @@
   ValueResult result;
   GetNamedValue(eval_context, "present", kQuitLoop, &result);
 
-  // Running the message loop should complete the callback.
-  loop().Run();
-
-  // The value should be not found.
+  // The value should be not found and this should be known synchronously.
   EXPECT_TRUE(result.called);
   EXPECT_TRUE(result.err.has_error());
   EXPECT_EQ(ExprValue(), result.value);
diff --git a/src/developer/debug/zxdb/expr/symbol_variable_resolver.cc b/src/developer/debug/zxdb/expr/symbol_variable_resolver.cc
index b164bab..4aba705 100644
--- a/src/developer/debug/zxdb/expr/symbol_variable_resolver.cc
+++ b/src/developer/debug/zxdb/expr/symbol_variable_resolver.cc
@@ -10,13 +10,11 @@
 
 #include "src/developer/debug/zxdb/expr/expr_value.h"
 #include "src/developer/debug/zxdb/expr/resolve_ptr_ref.h"
-#include "src/lib/fxl/strings/string_printf.h"
-#include "src/developer/debug/zxdb/expr/expr_value.h"
-#include "src/developer/debug/zxdb/expr/resolve_ptr_ref.h"
 #include "src/developer/debug/zxdb/symbols/symbol_context.h"
 #include "src/developer/debug/zxdb/symbols/symbol_data_provider.h"
 #include "src/developer/debug/zxdb/symbols/type.h"
 #include "src/developer/debug/zxdb/symbols/variable.h"
+#include "src/lib/fxl/strings/string_printf.h"
 
 namespace zxdb {
 
@@ -38,9 +36,13 @@
     return;
   }
 
-  auto ip = data_provider_->GetRegister(debug_ipc::GetSpecialRegisterID(
-      data_provider_->GetArch(), debug_ipc::SpecialRegisterType::kIP));
+  std::optional<uint64_t> ip;
+  data_provider_->GetRegister(
+      debug_ipc::GetSpecialRegisterID(data_provider_->GetArch(),
+                                      debug_ipc::SpecialRegisterType::kIP),
+      &ip);
   if (!ip) {
+    // The IP should never require an async call.
     OnComplete(state, Err("No location available."), ExprValue());
     return;
   }
diff --git a/src/developer/debug/zxdb/symbols/dwarf_expr_eval.cc b/src/developer/debug/zxdb/symbols/dwarf_expr_eval.cc
index 6893655..5e64cb6 100644
--- a/src/developer/debug/zxdb/symbols/dwarf_expr_eval.cc
+++ b/src/developer/debug/zxdb/symbols/dwarf_expr_eval.cc
@@ -9,13 +9,13 @@
 
 #include <utility>
 
-#include "src/lib/fxl/logging.h"
-#include "src/lib/fxl/strings/string_printf.h"
 #include "llvm/BinaryFormat/Dwarf.h"
 #include "llvm/Support/DataExtractor.h"
 #include "src/developer/debug/shared/message_loop.h"
 #include "src/developer/debug/zxdb/symbols/arch.h"
 #include "src/developer/debug/zxdb/symbols/symbol_data_provider.h"
+#include "src/lib/fxl/logging.h"
+#include "src/lib/fxl/strings/string_printf.h"
 
 namespace zxdb {
 
@@ -282,9 +282,15 @@
   // This function doesn't set the result_type_ because it is called from
   // different contexts. The callers should set the result_type_ as appropriate
   // for their operation.
-  if (auto reg_data = data_provider_->GetRegister(reg)) {
-    // Register data available synchronously.
-    Push(*reg_data + offset);
+  if (std::optional<uint64_t> reg_data;
+      data_provider_->GetRegister(reg, &reg_data)) {
+    // State known synchronously (could be available or known unavailable).
+    if (!reg_data) {
+      ReportError(fxl::StringPrintf("Register %d not available.",
+                                    dwarf_register_number));
+    } else {
+      Push(*reg_data + offset);
+    }
     return Completion::kSync;
   }
 
diff --git a/src/developer/debug/zxdb/symbols/mock_symbol_data_provider.cc b/src/developer/debug/zxdb/symbols/mock_symbol_data_provider.cc
index a559cb1b..af86946 100644
--- a/src/developer/debug/zxdb/symbols/mock_symbol_data_provider.cc
+++ b/src/developer/debug/zxdb/symbols/mock_symbol_data_provider.cc
@@ -8,10 +8,10 @@
 
 #include <algorithm>
 
-#include "src/lib/fxl/strings/string_printf.h"
 #include "src/developer/debug/ipc/protocol.h"
 #include "src/developer/debug/shared/message_loop.h"
 #include "src/developer/debug/zxdb/common/err.h"
+#include "src/lib/fxl/strings/string_printf.h"
 
 namespace zxdb {
 
@@ -32,19 +32,24 @@
   return debug_ipc::Arch::kArm64;
 }
 
-std::optional<uint64_t> MockSymbolDataProvider::GetRegister(
-    debug_ipc::RegisterID id) {
-  if (GetSpecialRegisterType(id) == debug_ipc::SpecialRegisterType::kIP)
-    return ip_;
+bool MockSymbolDataProvider::GetRegister(debug_ipc::RegisterID id,
+                                         std::optional<uint64_t>* value) {
+  *value = std::nullopt;
+
+  if (GetSpecialRegisterType(id) == debug_ipc::SpecialRegisterType::kIP) {
+    *value = ip_;
+    return true;
+  }
 
   const auto& found = regs_.find(id);
   if (found == regs_.end())
-    return std::nullopt;
+    return true;  // Known to be unknown.
 
   if (!found->second.synchronous)
-    return std::nullopt;  // Force synchronous query.
+    return false;
 
-  return found->second.value;
+  *value = found->second.value;
+  return true;
 }
 
 void MockSymbolDataProvider::GetRegisterAsync(debug_ipc::RegisterID id,
diff --git a/src/developer/debug/zxdb/symbols/mock_symbol_data_provider.h b/src/developer/debug/zxdb/symbols/mock_symbol_data_provider.h
index 095122c..ec19a4b9 100644
--- a/src/developer/debug/zxdb/symbols/mock_symbol_data_provider.h
+++ b/src/developer/debug/zxdb/symbols/mock_symbol_data_provider.h
@@ -2,12 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#pragma once
+#ifndef SRC_DEVELOPER_DEBUG_ZXDB_SYMBOLS_MOCK_SYMBOL_DATA_PROVIDER_H_
+#define SRC_DEVELOPER_DEBUG_ZXDB_SYMBOLS_MOCK_SYMBOL_DATA_PROVIDER_H_
 
 #include <map>
 
-#include "src/lib/fxl/memory/weak_ptr.h"
 #include "src/developer/debug/zxdb/symbols/symbol_data_provider.h"
+#include "src/lib/fxl/memory/weak_ptr.h"
 
 namespace zxdb {
 
@@ -25,6 +26,8 @@
   // Adds the given canned result for the given register. Set synchronous if
   // the register contents should be synchronously available, false if it
   // should require a callback to retrieve.
+  //
+  // Any registers not set will be synchronously reported as unknown.
   void AddRegisterValue(debug_ipc::RegisterID id, bool synchronous,
                         uint64_t value);
 
@@ -37,7 +40,8 @@
 
   // SymbolDataProvider implementation.
   debug_ipc::Arch GetArch() override;
-  std::optional<uint64_t> GetRegister(debug_ipc::RegisterID id) override;
+  bool GetRegister(debug_ipc::RegisterID id,
+                   std::optional<uint64_t>* value) override;
   void GetRegisterAsync(debug_ipc::RegisterID id,
                         GetRegisterCallback callback) override;
   std::optional<uint64_t> GetFrameBase() override;
@@ -75,3 +79,5 @@
 };
 
 }  // namespace zxdb
+
+#endif  // SRC_DEVELOPER_DEBUG_ZXDB_SYMBOLS_MOCK_SYMBOL_DATA_PROVIDER_H_
diff --git a/src/developer/debug/zxdb/symbols/module_symbols_impl.cc b/src/developer/debug/zxdb/symbols/module_symbols_impl.cc
index 4b04fec..44b4d0ea 100644
--- a/src/developer/debug/zxdb/symbols/module_symbols_impl.cc
+++ b/src/developer/debug/zxdb/symbols/module_symbols_impl.cc
@@ -48,15 +48,11 @@
 
   // SymbolDataProvider implementation.
   debug_ipc::Arch GetArch() override { return debug_ipc::Arch::kUnknown; }
-  std::optional<uint64_t> GetRegister(debug_ipc::RegisterID) override {
-    return std::nullopt;
-  }
   void GetRegisterAsync(debug_ipc::RegisterID,
                         GetRegisterCallback callback) override {
     debug_ipc::MessageLoop::Current()->PostTask(
         FROM_HERE, [cb = std::move(callback)]() { cb(GetContextError(), 0); });
   }
-  std::optional<uint64_t> GetFrameBase() override { return std::nullopt; }
   void GetFrameBaseAsync(GetRegisterCallback callback) override {
     debug_ipc::MessageLoop::Current()->PostTask(
         FROM_HERE, [cb = std::move(callback)]() { cb(GetContextError(), 0); });
diff --git a/src/developer/debug/zxdb/symbols/symbol_data_provider.cc b/src/developer/debug/zxdb/symbols/symbol_data_provider.cc
index fad581f..b56b67c 100644
--- a/src/developer/debug/zxdb/symbols/symbol_data_provider.cc
+++ b/src/developer/debug/zxdb/symbols/symbol_data_provider.cc
@@ -20,9 +20,10 @@
   return debug_ipc::Arch::kUnknown;
 }
 
-std::optional<uint64_t> SymbolDataProvider::GetRegister(
-    debug_ipc::RegisterID id) {
-  return std::nullopt;
+bool SymbolDataProvider::GetRegister(debug_ipc::RegisterID id,
+                                     std::optional<uint64_t>* value) {
+  *value = std::nullopt;
+  return true;  // Known to be unknown.
 }
 
 void SymbolDataProvider::GetRegisterAsync(debug_ipc::RegisterID,
diff --git a/src/developer/debug/zxdb/symbols/symbol_data_provider.h b/src/developer/debug/zxdb/symbols/symbol_data_provider.h
index ce071fb5..76073af 100644
--- a/src/developer/debug/zxdb/symbols/symbol_data_provider.h
+++ b/src/developer/debug/zxdb/symbols/symbol_data_provider.h
@@ -2,7 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#pragma once
+#ifndef SRC_DEVELOPER_DEBUG_ZXDB_SYMBOLS_SYMBOL_DATA_PROVIDER_H_
+#define SRC_DEVELOPER_DEBUG_ZXDB_SYMBOLS_SYMBOL_DATA_PROVIDER_H_
 
 #include <stdint.h>
 
@@ -10,8 +11,8 @@
 #include <optional>
 #include <vector>
 
-#include "src/lib/fxl/memory/ref_counted.h"
 #include "src/developer/debug/ipc/protocol.h"
+#include "src/lib/fxl/memory/ref_counted.h"
 
 namespace zxdb {
 
@@ -42,10 +43,17 @@
 
   virtual debug_ipc::Arch GetArch();
 
-  // Request for synchronous register data. If the register data can be provided
-  // synchronously, the data will be returned. If synchronous data is not
-  // available, the caller should call GetRegisterAsync().
-  virtual std::optional<uint64_t> GetRegister(debug_ipc::RegisterID id);
+  // Request for synchronous register data. If the value is not synchronously
+  // availble, the *value will always be a nullopt.
+  //
+  // A return value of false means that the value is not known synchronously.
+  // In this case, GetRegisterAsync should be called to retrieve the value.
+  //
+  // In the synchronous case, we could have the value, but we could also know
+  // that the value is not known (e.g. when that register was not saved for the
+  // stack frame). The *value will reflect this when the return value is true.
+  virtual bool GetRegister(debug_ipc::RegisterID id,
+                           std::optional<uint64_t>* value);
 
   // Request for register data with an asynchronous callback. The callback will
   // be issued when the register data is available.
@@ -94,3 +102,5 @@
 };
 
 }  // namespace zxdb
+
+#endif  // SRC_DEVELOPER_DEBUG_ZXDB_SYMBOLS_SYMBOL_DATA_PROVIDER_H_