diff --git a/src/Device/Port/BufferedPort.cpp b/src/Device/Port/BufferedPort.cpp
index 1bf9741df84..0eb5a707a36 100644
--- a/src/Device/Port/BufferedPort.cpp
+++ b/src/Device/Port/BufferedPort.cpp
@@ -60,7 +60,7 @@ BufferedPort::StartRxThread()
   return true;
 }
 
-int
+std::size_t
 BufferedPort::Read(void *dest, std::size_t length)
 {
   assert(!running);
@@ -68,9 +68,6 @@ BufferedPort::Read(void *dest, std::size_t length)
   std::lock_guard<Mutex> lock(mutex);
 
   auto r = buffer.Read();
-  if (r.size == 0)
-    return -1;
-
   std::size_t nbytes = std::min(length, r.size);
   std::copy_n(r.data, nbytes, (std::byte *)dest);
   buffer.Consume(nbytes);
diff --git a/src/Device/Port/BufferedPort.hpp b/src/Device/Port/BufferedPort.hpp
index d36248eacf1..7a95ccb5f36 100644
--- a/src/Device/Port/BufferedPort.hpp
+++ b/src/Device/Port/BufferedPort.hpp
@@ -60,7 +60,7 @@ class BufferedPort : public Port, protected DataHandler {
 public:
   /* virtual methods from class Port */
   void Flush() override;
-  int Read(void *Buffer, std::size_t Size) override;
+  std::size_t Read(void *Buffer, std::size_t Size) override;
   void WaitRead(std::chrono::steady_clock::duration timeout) override;
   bool StopRxThread() override;
   bool StartRxThread() override;
diff --git a/src/Device/Port/DumpPort.cpp b/src/Device/Port/DumpPort.cpp
index ebad2d35395..f8871e0c755 100644
--- a/src/Device/Port/DumpPort.cpp
+++ b/src/Device/Port/DumpPort.cpp
@@ -143,17 +143,17 @@ DumpPort::StartRxThread()
   return port->StartRxThread();
 }
 
-int
+std::size_t
 DumpPort::Read(void *buffer, std::size_t size)
 {
   const bool enabled = CheckEnabled();
   if (enabled)
     LogFormat("Read(%u)", (unsigned)size);
 
-  int nbytes = port->Read(buffer, size);
+  auto nbytes = port->Read(buffer, size);
 
   if (enabled) {
-    LogFormat("Read(%u)=%d", (unsigned)size, nbytes);
+    LogFormat("Read(%u)=%u", (unsigned)size, (unsigned)nbytes);
     if (nbytes > 0)
       HexDump("R ", buffer, nbytes);
   }
diff --git a/src/Device/Port/DumpPort.hpp b/src/Device/Port/DumpPort.hpp
index 9aa4cbf7358..5eb6026ab85 100644
--- a/src/Device/Port/DumpPort.hpp
+++ b/src/Device/Port/DumpPort.hpp
@@ -90,7 +90,7 @@ class DumpPort final : public Port {
   void SetBaudrate(unsigned baud_rate) override;
   bool StopRxThread() override;
   bool StartRxThread() override;
-  int Read(void *buffer, std::size_t size) override;
+  std::size_t Read(void *buffer, std::size_t size) override;
   void WaitRead(std::chrono::steady_clock::duration timeout) override;
 };
 
diff --git a/src/Device/Port/K6BtPort.cpp b/src/Device/Port/K6BtPort.cpp
index aed5826f71f..fe1bc12a972 100644
--- a/src/Device/Port/K6BtPort.cpp
+++ b/src/Device/Port/K6BtPort.cpp
@@ -180,7 +180,7 @@ K6BtPort::StartRxThread(void)
   return port->StartRxThread();
 }
 
-int
+std::size_t
 K6BtPort::Read(void *Buffer, std::size_t Size)
 {
   return port->Read(Buffer, Size);
diff --git a/src/Device/Port/K6BtPort.hpp b/src/Device/Port/K6BtPort.hpp
index 6d0572a0524..5735ab6c840 100644
--- a/src/Device/Port/K6BtPort.hpp
+++ b/src/Device/Port/K6BtPort.hpp
@@ -63,7 +63,7 @@ class K6BtPort : public Port {
   unsigned GetBaudrate() const noexcept override;
   bool StopRxThread() override;
   bool StartRxThread() override;
-  int Read(void *Buffer, std::size_t Size) override;
+  std::size_t Read(void *Buffer, std::size_t Size) override;
   void WaitRead(std::chrono::steady_clock::duration timeout) override;
 };
 
diff --git a/src/Device/Port/NullPort.cpp b/src/Device/Port/NullPort.cpp
index 69117e0f8a7..fb9a04dd821 100644
--- a/src/Device/Port/NullPort.cpp
+++ b/src/Device/Port/NullPort.cpp
@@ -83,10 +83,10 @@ NullPort::SetBaudrate(unsigned)
 {
 }
 
-int
+std::size_t
 NullPort::Read(void *Buffer, std::size_t Size)
 {
-  return -1;
+  return 0;
 }
 
 void
diff --git a/src/Device/Port/NullPort.hpp b/src/Device/Port/NullPort.hpp
index ac269b49326..932f6f4496f 100644
--- a/src/Device/Port/NullPort.hpp
+++ b/src/Device/Port/NullPort.hpp
@@ -44,7 +44,7 @@ class NullPort : public Port, private DataHandler  {
   void SetBaudrate(unsigned baud_rate) override;
   bool StopRxThread() override;
   bool StartRxThread() override;
-  int Read(void *Buffer, std::size_t Size) override;
+  std::size_t Read(void *Buffer, std::size_t Size) override;
 
   [[noreturn]]
   void WaitRead(std::chrono::steady_clock::duration timeout) override;
diff --git a/src/Device/Port/Port.hpp b/src/Device/Port/Port.hpp
index 673beab74c2..763caf5a669 100644
--- a/src/Device/Port/Port.hpp
+++ b/src/Device/Port/Port.hpp
@@ -167,10 +167,11 @@ class Port {
    * Read data from the serial port
    * @param Buffer Pointer to the buffer
    * @param Size Size of the buffer
-   * @return Number of bytes read from the serial port or -1 on failure
+   * @return Number of bytes read from the port (0 if no data is
+   * available currently)
    */
   gcc_nonnull_all
-  virtual int Read(void *Buffer, std::size_t Size) = 0;
+  virtual std::size_t Read(void *Buffer, std::size_t Size) = 0;
 
   /**
    * Wait until data becomes available or the timeout expires.
diff --git a/test/src/FaultInjectionPort.hpp b/test/src/FaultInjectionPort.hpp
index 7579cb9d264..583d2570a6c 100644
--- a/test/src/FaultInjectionPort.hpp
+++ b/test/src/FaultInjectionPort.hpp
@@ -79,9 +79,9 @@ class FaultInjectionPort : public Port {
     return true;
   }
 
-  int Read(void *Buffer, size_t Size) override {
+  std::size_t Read(void *Buffer, size_t Size) override {
     if (inject_port_fault == 0)
-      return -1;
+      return 0;
 
     if (--inject_port_fault == 0)
       StateChanged();
diff --git a/test/src/ReadPort.cpp b/test/src/ReadPort.cpp
index fd1770f4337..ac71ff873a6 100644
--- a/test/src/ReadPort.cpp
+++ b/test/src/ReadPort.cpp
@@ -64,10 +64,7 @@ try {
       continue;
     }
 
-    int nbytes = port->Read(buffer, sizeof(buffer));
-    if (nbytes < 0)
-      break;
-
+    std::size_t nbytes = port->Read(buffer, sizeof(buffer));
     fwrite((const void *)buffer, 1, nbytes, stdout);
   }