diff --git a/native_client/deepspeech.cc b/native_client/deepspeech.cc
index c500fc83..539cafd2 100644
--- a/native_client/deepspeech.cc
+++ b/native_client/deepspeech.cc
@@ -77,7 +77,7 @@ struct StreamingState {
   ~StreamingState();
 
   void feedAudioContent(const short* buffer, unsigned int buffer_size);
-  char* intermediateDecode();
+  char* intermediateDecode() const;
   void finalizeStream();
   char* finishStream();
   Metadata* finishStreamWithMetadata();
@@ -131,7 +131,7 @@ StreamingState::feedAudioContent(const short* buffer,
 }
 
 char*
-StreamingState::intermediateDecode()
+StreamingState::intermediateDecode() const
 {
   return model_->decode(decoder_state_);
 }
@@ -298,7 +298,7 @@ DS_CreateModel(const char* aModelPath,
 }
 
 unsigned int
-DS_GetModelBeamWidth(ModelState* aCtx)
+DS_GetModelBeamWidth(const ModelState* aCtx)
 {
   return aCtx->beam_width_;
 }
@@ -311,7 +311,7 @@ DS_SetModelBeamWidth(ModelState* aCtx, unsigned int aBeamWidth)
 }
 
 int
-DS_GetModelSampleRate(ModelState* aCtx)
+DS_GetModelSampleRate(const ModelState* aCtx)
 {
   return aCtx->sample_rate_;
 }
@@ -397,7 +397,7 @@ DS_FeedAudioContent(StreamingState* aSctx,
 }
 
 char*
-DS_IntermediateDecode(StreamingState* aSctx)
+DS_IntermediateDecode(const StreamingState* aSctx)
 {
   return aSctx->intermediateDecode();
 }
diff --git a/native_client/deepspeech.h b/native_client/deepspeech.h
index 53e93ec3..ca20c011 100644
--- a/native_client/deepspeech.h
+++ b/native_client/deepspeech.h
@@ -96,7 +96,7 @@ int DS_CreateModel(const char* aModelPath,
  * @return Beam width value used by the model.
  */
 DEEPSPEECH_EXPORT
-unsigned int DS_GetModelBeamWidth(ModelState* aCtx);
+unsigned int DS_GetModelBeamWidth(const ModelState* aCtx);
 
 /**
  * @brief Set beam width value used by the model.
@@ -119,7 +119,7 @@ int DS_SetModelBeamWidth(ModelState* aCtx,
  * @return Sample rate expected by the model for its input.
  */
 DEEPSPEECH_EXPORT
-int DS_GetModelSampleRate(ModelState* aCtx);
+int DS_GetModelSampleRate(const ModelState* aCtx);
 
 /**
  * @brief Frees associated resources and destroys model object.
@@ -233,7 +233,7 @@ void DS_FeedAudioContent(StreamingState* aSctx,
  *         string using {@link DS_FreeString()}.
  */
 DEEPSPEECH_EXPORT
-char* DS_IntermediateDecode(StreamingState* aSctx);
+char* DS_IntermediateDecode(const StreamingState* aSctx);
 
 /**
  * @brief Signal the end of an audio signal to an ongoing streaming
diff --git a/native_client/modelstate.cc b/native_client/modelstate.cc
index 4bc0e953..ea8928bd 100644
--- a/native_client/modelstate.cc
+++ b/native_client/modelstate.cc
@@ -30,7 +30,7 @@ ModelState::init(const char* model_path)
 }
 
 char*
-ModelState::decode(const DecoderState& state)
+ModelState::decode(const DecoderState& state) const
 {
   vector<Output> out = state.decode();
   return strdup(alphabet_.LabelsToString(out[0].tokens).c_str());
diff --git a/native_client/modelstate.h b/native_client/modelstate.h
index c296c003..25251e15 100644
--- a/native_client/modelstate.h
+++ b/native_client/modelstate.h
@@ -60,7 +60,7 @@ struct ModelState {
    *
    * @return String representing the decoded text.
    */
-  virtual char* decode(const DecoderState& state);
+  virtual char* decode(const DecoderState& state) const;
 
   /**
    * @brief Return character-level metadata including letter timings.