diff --git a/src/printf.cpp b/src/printf.cpp
index 9cf2c08..ac4b92a 100644
--- a/src/printf.cpp
+++ b/src/printf.cpp
@@ -18,12 +18,12 @@
 */
 
 /*
-	putchar is the only external dependency for this file,
-	if you have a working putchar, leave it commented out.
+	libopeninv_putchar is the only external dependency for this file,
+	if you have a working libopeninv_putchar, leave it commented out.
 	If not, uncomment the define below and
 	replace outbyte(c) by your own function call.
 
-#define putchar(c) outbyte(c)
+#define libopeninv_putchar(c) outbyte(c)
 */
 
 #include <stdarg.h>
@@ -35,14 +35,14 @@
 #define PAD_RIGHT 1
 #define PAD_ZERO 2
 
-extern "C" void putchar(char c);
+extern "C" void libopeninv_putchar(int c);
 
 class ExternPutChar: public IPutChar
 {
 public:
    void PutChar(char c)
    {
-      putchar(c);
+      libopeninv_putchar(c);
    }
 };
 
diff --git a/src/terminal.cpp b/src/terminal.cpp
index 0a2d771..2723e43 100644
--- a/src/terminal.cpp
+++ b/src/terminal.cpp
@@ -359,7 +359,8 @@ void Terminal::SendCurrentBuffer(uint32_t len)
 }
 
 //Backward compatibility for printf
-extern "C" void putchar(int c)
+extern "C" void libopeninv_putchar(int c)
 {
-   Terminal::defaultTerminal->PutChar(c);
+   if (Terminal::defaultTerminal != nullptr)
+      Terminal::defaultTerminal->PutChar(c);
 }
diff --git a/test/stub_canhardware.h b/test/stub_canhardware.h
index 13331cb..2fd5947 100644
--- a/test/stub_canhardware.h
+++ b/test/stub_canhardware.h
@@ -28,8 +28,9 @@
 class CanStub: public CanHardware
 {
    void SetBaudrate(enum baudrates baudrate) {}
-   void Send(uint32_t canId, uint32_t data[2], uint8_t len)
+   void Send(uint32_t canId, uint32_t data[2], uint8_t len, bool forceExt) override
    {
+      (void)forceExt;
       m_canId = canId;
       memcpy(&m_data[0], &data[0], sizeof(m_data));
       m_len = len;
@@ -45,4 +46,4 @@ class CanStub: public CanHardware
 extern CanCallback* vcuCan;
 extern uint32_t vcuCanId;
 
-#endif // TEST_CANHARDWARE_H
\ No newline at end of file
+#endif // TEST_CANHARDWARE_H
diff --git a/test/stub_libopencm3.c b/test/stub_libopencm3.c
index 8165bd1..b90a35b 100644
--- a/test/stub_libopencm3.c
+++ b/test/stub_libopencm3.c
@@ -147,3 +147,7 @@ void dma_enable_channel(uint32_t dma, uint8_t channel)
 void dma_disable_channel(uint32_t dma, uint8_t channel)
 {
 }
+
+void libopeninv_putchar(int c)
+{
+}
diff --git a/test/test_cansdo.cpp b/test/test_cansdo.cpp
index c54d5c6..dff4b06 100644
--- a/test/test_cansdo.cpp
+++ b/test/test_cansdo.cpp
@@ -30,10 +30,12 @@ class IPutChar { public: virtual void PutChar(char c) = 0; };
 #include "my_fp.h"
 #include "stub_canhardware.h"
 #include "test.h"
+#include "sdocommands.h"
 
 #include <memory>
 #include <cstdint>
 
+
 class CanSdoTest : public UnitTest
 {
 public:
@@ -41,15 +43,47 @@ class CanSdoTest : public UnitTest
     virtual void TestCaseSetup();
 };
 
+class UserSpaceCanSdo : public CanSdo
+{
+public:
+    explicit UserSpaceCanSdo(CanHardware* hw, CanMap* cm = nullptr) : CanSdo(hw, cm) {}
+
+    bool shouldHandleUserSpaceSdo = false;
+    bool wasUserSpaceCalled = false;
+    SdoFrame lastUserSpaceRequest{};
+
+    bool ProcessUserSpaceSdo(SdoFrame* sdo) override
+    {
+        wasUserSpaceCalled = true;
+        lastUserSpaceRequest = *sdo;
+
+        if (shouldHandleUserSpaceSdo)
+        {
+            sdo->cmd = SDO_WRITE_REPLY;
+            sdo->data = 0;
+            return true;
+        }
+
+        return false;
+    }
+};
+
 static std::unique_ptr<CanStub> canStub;
 static std::unique_ptr<CanMap>  canMap;
-static std::unique_ptr<CanSdo>  canSdo;
+static std::unique_ptr<UserSpaceCanSdo>  canSdo;
+CanMap* SdoCommands::canMap;
+
+void SdoCommands::ProcessStandardCommands(CanSdo::SdoFrame* sdoFrame)
+{
+   sdoFrame->cmd = SDO_ABORT;
+   sdoFrame->data = SDO_ERR_INVIDX;
+}
 
 void CanSdoTest::TestCaseSetup()
 {
     canStub = std::make_unique<CanStub>();
     canMap  = std::make_unique<CanMap>(canStub.get(), false);
-    canSdo  = std::make_unique<CanSdo>(canStub.get(), canMap.get());
+    canSdo  = std::make_unique<UserSpaceCanSdo>(canStub.get(), canMap.get());
     Param::LoadDefaults();
 }
 
@@ -383,30 +417,26 @@ static void sdo_write_error_time_aborts()
 
 static void sdo_unknown_index_goes_to_user_space()
 {
-    // Index 0x4000 is not handled by CanSdo itself
+    // Index 0x4000 is not handled internally and is offered to user-space first.
+    canSdo->shouldHandleUserSpaceSdo = false;
     SendSdoRequest(SDO_WRITE, 0x4000, 0, 0xDEADBEEF);
 
-    // No CAN reply should be sent; the pending user-space SDO should be set
-    CanSdo::SdoFrame* pending = canSdo->GetPendingUserspaceSdo();
-    ASSERT(pending != nullptr);
-    ASSERT(pending->index == 0x4000);
-    ASSERT(pending->data == 0xDEADBEEF);
+    ASSERT(canSdo->wasUserSpaceCalled);
+    ASSERT(canSdo->lastUserSpaceRequest.index == 0x4000);
+    ASSERT(canSdo->lastUserSpaceRequest.data == 0xDEADBEEF);
+    ASSERT(canStub->m_canId == SdoRepId);
+    ASSERT(GetReply()->cmd == SDO_ABORT);
+    ASSERT(GetReply()->data == SDO_ERR_INVIDX);
 }
 
 static void sdo_reply_sent_via_send_sdo_reply()
 {
+    canSdo->shouldHandleUserSpaceSdo = true;
     SendSdoRequest(SDO_WRITE, 0x4000, 0, 0x1234);
 
-    CanSdo::SdoFrame* pending = canSdo->GetPendingUserspaceSdo();
-    ASSERT(pending != nullptr);
-
-    // User space fills in the reply and calls SendSdoReply
-    pending->cmd  = SDO_WRITE_REPLY;
-    pending->data = 0;
-    canSdo->SendSdoReply(pending);
-
-    // After sending the reply, the pending flag must be cleared
-    ASSERT(canSdo->GetPendingUserspaceSdo() == nullptr);
+    ASSERT(canSdo->wasUserSpaceCalled);
+    ASSERT(canSdo->lastUserSpaceRequest.index == 0x4000);
+    ASSERT(canSdo->lastUserSpaceRequest.data == 0x1234);
     ASSERT(canStub->m_canId == SdoRepId);
     ASSERT(GetReply()->cmd == SDO_WRITE_REPLY);
 }