diff --git a/lib/compress/zstd_compress.c b/lib/compress/zstd_compress.c
index f5ac75a..1df1a48 100644
--- a/lib/compress/zstd_compress.c
+++ b/lib/compress/zstd_compress.c
@@ -2753,23 +2753,26 @@
 }
 
 
+/* ZSTD_selectBlockCompressor() :
+ * assumption : strat is a valid strategy */
 typedef void (*ZSTD_blockCompressor) (ZSTD_CCtx* ctx, const void* src, size_t srcSize);
-
 static ZSTD_blockCompressor ZSTD_selectBlockCompressor(ZSTD_strategy strat, int extDict)
 {
     static const ZSTD_blockCompressor blockCompressor[2][(unsigned)ZSTD_btultra+1] = {
-        { NULL,
+        { ZSTD_compressBlock_fast  /* default for 0 */,
           ZSTD_compressBlock_fast, ZSTD_compressBlock_doubleFast, ZSTD_compressBlock_greedy,
           ZSTD_compressBlock_lazy, ZSTD_compressBlock_lazy2, ZSTD_compressBlock_btlazy2,
           ZSTD_compressBlock_btopt, ZSTD_compressBlock_btultra },
-        { NULL,
+        { ZSTD_compressBlock_fast_extDict  /* default for 0 */,
           ZSTD_compressBlock_fast_extDict, ZSTD_compressBlock_doubleFast_extDict, ZSTD_compressBlock_greedy_extDict,
           ZSTD_compressBlock_lazy_extDict,ZSTD_compressBlock_lazy2_extDict, ZSTD_compressBlock_btlazy2_extDict,
           ZSTD_compressBlock_btopt_extDict, ZSTD_compressBlock_btultra_extDict }
     };
     ZSTD_STATIC_ASSERT((unsigned)ZSTD_fast == 1);
+    assert((U32)strat >= (U32)ZSTD_fast);
+    assert((U32)strat <= (U32)ZSTD_btultra);
 
-    return blockCompressor[extDict][(U32)strat];
+    return blockCompressor[extDict!=0][(U32)strat];
 }
 
 
diff --git a/lib/compress/zstdmt_compress.h b/lib/compress/zstdmt_compress.h
index 8b0ca82..d36914d 100644
--- a/lib/compress/zstdmt_compress.h
+++ b/lib/compress/zstdmt_compress.h
@@ -15,13 +15,15 @@
  #endif
 
 
-/* Note : All prototypes defined in this file must be considered experimental.
- *        There is no guarantee of API continuity on any of these prototypes */
+/* Note : All prototypes defined in this file are labelled experimental.
+ *        No guarantee of API continuity is provided on any of them.
+ *        In fact, the expectation is that these prototypes will be replaced
+ *        by ZSTD_compress_generic() API in the near future */
 
 /* ===   Dependencies   === */
-#include <stddef.h>   /* size_t */
+#include <stddef.h>                /* size_t */
 #define ZSTD_STATIC_LINKING_ONLY   /* ZSTD_parameters */
-#include "zstd.h"     /* ZSTD_inBuffer, ZSTD_outBuffer, ZSTDLIB_API */
+#include "zstd.h"            /* ZSTD_inBuffer, ZSTD_outBuffer, ZSTDLIB_API */
 
 
 /* ===   Memory management   === */
@@ -32,7 +34,6 @@
 ZSTDLIB_API size_t ZSTDMT_freeCCtx(ZSTDMT_CCtx* mtctx);
 
 ZSTDLIB_API size_t ZSTDMT_sizeof_CCtx(ZSTDMT_CCtx* mtctx);
-ZSTDLIB_API size_t ZSTDMT_estimateCCtxSize(ZSTD_compressionParameters cParams, unsigned nbThreads);   /* not ready yet */
 
 
 /* ===   Simple buffer-to-butter one-pass function   === */
@@ -87,7 +88,7 @@
 
 /*! ZSTDMT_compressStream_generic() :
  *  Combines ZSTDMT_compressStream() with ZSTDMT_flushStream() or ZSTDMT_endStream()
- *  depending on flush directive
+ *  depending on flush directive.
  * @return : minimum amount of data still to be flushed
  *           0 if fully flushed
  *           or an error code */