diff --git a/httplib.h b/httplib.h
index 150067e..097224b 100644
--- a/httplib.h
+++ b/httplib.h
@@ -735,6 +735,10 @@ public:
   virtual bool is_readable() const = 0;
   virtual bool is_writable() const = 0;
 
+  // Returns maximum size that may be passed to read() without blocking; read()
+  // may return fewer bytes
+  virtual size_t nonblocking_read_size() const = 0;
+
   virtual ssize_t read(char *ptr, size_t size) = 0;
   virtual ssize_t write(const char *ptr, size_t size) = 0;
   virtual void get_remote_ip_and_port(std::string &ip, int &port) const = 0;
@@ -2384,6 +2388,7 @@ public:
 
   bool is_readable() const override;
   bool is_writable() const override;
+  size_t nonblocking_read_size() const override;
   ssize_t read(char *ptr, size_t size) override;
   ssize_t write(const char *ptr, size_t size) override;
   void get_remote_ip_and_port(std::string &ip, int &port) const override;
@@ -3311,6 +3316,7 @@ public:
 
   bool is_readable() const override;
   bool is_writable() const override;
+  size_t nonblocking_read_size() const override;
   ssize_t read(char *ptr, size_t size) override;
   ssize_t write(const char *ptr, size_t size) override;
   void get_remote_ip_and_port(std::string &ip, int &port) const override;
@@ -3341,6 +3347,7 @@ public:
 
   bool is_readable() const override;
   bool is_writable() const override;
+  size_t nonblocking_read_size() const override;
   ssize_t read(char *ptr, size_t size) override;
   ssize_t write(const char *ptr, size_t size) override;
   void get_remote_ip_and_port(std::string &ip, int &port) const override;
@@ -5977,6 +5984,10 @@ inline bool SocketStream::is_writable() const {
          is_socket_alive(sock_);
 }
 
+inline size_t SocketStream::nonblocking_read_size() const {
+  return read_buff_content_size_ - read_buff_off_;
+}
+
 inline ssize_t SocketStream::read(char *ptr, size_t size) {
 #ifdef _WIN32
   size =
@@ -6051,6 +6062,10 @@ inline bool BufferStream::is_readable() const { return true; }
 
 inline bool BufferStream::is_writable() const { return true; }
 
+inline size_t BufferStream::nonblocking_read_size() const {
+  return (std::numeric_limits<size_t>::max)();
+}
+
 inline ssize_t BufferStream::read(char *ptr, size_t size) {
 #if defined(_MSC_VER) && _MSC_VER < 1910
   auto len_read = buffer._Copy_s(ptr, size, size, position);
@@ -9121,6 +9136,10 @@ inline bool SSLSocketStream::is_writable() const {
          is_socket_alive(sock_);
 }
 
+inline size_t SSLSocketStream::nonblocking_read_size() const {
+  return static_cast<size_t>(SSL_pending(ssl_));
+}
+
 inline ssize_t SSLSocketStream::read(char *ptr, size_t size) {
   if (SSL_pending(ssl_) > 0) {
     return SSL_read(ssl_, ptr, static_cast<int>(size));
diff --git a/test/fuzzing/server_fuzzer.cc b/test/fuzzing/server_fuzzer.cc
index 3cffbae..8424246 100644
--- a/test/fuzzing/server_fuzzer.cc
+++ b/test/fuzzing/server_fuzzer.cc
@@ -1,4 +1,5 @@
 #include <cstdint>
+#include <limits>
 
 #include <httplib.h>
 
@@ -27,6 +28,8 @@ public:
 
   bool is_writable() const override { return true; }
 
+  size_t nonblocking_read_size() const override { return (std::numeric_limits<size_t>::max)(); }
+
   void get_remote_ip_and_port(std::string &ip, int &port) const override {
     ip = "127.0.0.1";
     port = 8080;