C++ protected function not visible from derived class

I'm trying to call initCapture() that's declared pure virtual in LexContext. I'm trying to call it indirectly in ArduinoLexContext by way of StaticLexContext which overrides it.

I get

LexContext.hpp:316:25: error: there are no arguments to 'initCapture' that depend on a template parameter, so a declaration of 'initCapture' must be available [-fpermissive]

Here's the code. I've omitted most of LexContext since it isn't relevant here. I've been at this all morning and I know the answer is staring me right in the face but I need another set of eyes on this.

Thanks in advance.

#include <cstdint>
#include <ctype.h>
#include <stdlib.h>
namespace lex {
  // represents a cursor and capture buffer over an input source
  class LexContext {
      int16_t _current;
      unsigned long int _line;
      unsigned long int _column;
      unsigned long long _position;
    protected:
      // reads a character from the underlying device
      // read() should return EndOfInput if no more data is available,
      // and Closed if the underlying source has been closed, where
      // applicable
      virtual int16_t read()=0;
      // called to initialize the capture buffer
      virtual void initCapture()=0;
    public:
      ...

  };
// represents a LexContext with a fixed size buffer
  template<const size_t S> class StaticLexContext : virtual public LexContext {
    char _capture[S];
    size_t _captureCount;
    protected:
      // initializes the capture buffer
      void initCapture() override {
        *_capture=0;
        _captureCount=0;

      }
    public:
      StaticLexContext() {
            
      }
      // the capacity of the capture buffer (not including the trailing NULL)
      size_t captureCapacity() override { return S-1; }
      // the count of characters in the capture buffer
      size_t captureCount() const override {return _captureCount;}
      // returns a pointer to the capture buffer
      char* captureBuffer() override {return _capture;}
      // clears the capture buffer
      void clearCapture() override {
        _captureCount = 0;
        *_capture=0;
      }
      // captures the character under the cursor if any
      // returns true if a character was captured.
      bool capture() override {
        if (Closed!=current() && EndOfInput != current() && BeforeInput != current() && (S - 1) > _captureCount)
        {
          _capture[_captureCount++] = (uint8_t)current();
          _capture[_captureCount] = 0;
          return true;
        }
        return false;
      }

  };
#ifdef ARDUINO
  // represents a fixed length LexContext for the Arduino built on the Arduino SDK's Stream class
  template<const size_t S> class ArduinoLexContext : public StaticLexContext<S> { 
        Stream* _pstream;
    protected:
        // reads a character from the stream
        int16_t read() override {
            if(!_pstream)
              return LexContext::Closed;
            return _pstream->read();
        }
    public:
      ArduinoLexContext() {
            
      }
        // initializes the lexcontext with a stream
        bool begin(Stream& stream) {
            _pstream = &stream;
            initCapture(); // compile error!
            return true;
        }
    };
#endif
}