diff --git a/lib/compress/zstd_compress.c b/lib/compress/zstd_compress.c
index 1d59279e3..1b380d3fe 100644
--- a/lib/compress/zstd_compress.c
+++ b/lib/compress/zstd_compress.c
@@ -113,6 +113,7 @@ size_t ZSTD_freeCCtx(ZSTD_CCtx* cctx)
 
 size_t ZSTD_sizeof_CCtx(const ZSTD_CCtx* cctx)
 {
+    if (cctx==NULL) return 0;   /* support sizeof on NULL */
     return sizeof(*cctx) + cctx->workSpaceSize;
 }
 
@@ -2680,6 +2681,12 @@ struct ZSTD_CDict_s {
     ZSTD_CCtx* refContext;
 };  /* typedef'd tp ZSTD_CDict within "zstd.h" */
 
+size_t ZSTD_sizeof_CDict(const ZSTD_CDict* cdict)
+{
+    if (cdict==NULL) return 0;   /* support sizeof on NULL */
+    return ZSTD_sizeof_CCtx(cdict->refContext) + cdict->dictContentSize;
+}
+
 ZSTD_CDict* ZSTD_createCDict_advanced(const void* dict, size_t dictSize, ZSTD_parameters params, ZSTD_customMem customMem)
 {
     if (!customMem.customAlloc && !customMem.customFree) customMem = defaultCustomMem;
@@ -2862,6 +2869,7 @@ size_t ZSTD_initCStream(ZSTD_CStream* zcs, int compressionLevel)
 
 size_t ZSTD_sizeof_CStream(const ZSTD_CStream* zcs)
 {
+    if (zcs==NULL) return 0;   /* support sizeof on NULL */
     return sizeof(zcs) + ZSTD_sizeof_CCtx(zcs->zc) + zcs->outBuffSize + zcs->inBuffSize;
 }
 
diff --git a/lib/decompress/zstd_decompress.c b/lib/decompress/zstd_decompress.c
index 1ea330bed..2b2539a4a 100644
--- a/lib/decompress/zstd_decompress.c
+++ b/lib/decompress/zstd_decompress.c
@@ -111,7 +111,7 @@ struct ZSTD_DCtx_s
     BYTE headerBuffer[ZSTD_FRAMEHEADERSIZE_MAX];
 };  /* typedef'd to ZSTD_DCtx within "zstd.h" */
 
-size_t ZSTD_sizeof_DCtx (const ZSTD_DCtx* dctx) { return sizeof(*dctx); }
+size_t ZSTD_sizeof_DCtx (const ZSTD_DCtx* dctx) { if (dctx==NULL) return 0; return sizeof(ZSTD_DCtx); }  /* support sizeof on NULL */
 
 size_t ZSTD_estimateDCtxSize(void) { return sizeof(ZSTD_DCtx); }
 
@@ -1251,6 +1251,7 @@ size_t ZSTD_freeDDict(ZSTD_DDict* ddict)
 
 size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict)
 {
+    if (ddict==NULL) return 0;   /* support sizeof on NULL */
     return sizeof(*ddict) + sizeof(ddict->refContext) + ddict->dictSize;
 }
 
@@ -1390,6 +1391,7 @@ size_t ZSTD_setDStreamParameter(ZSTD_DStream* zds,
 
 size_t ZSTD_sizeof_DStream(const ZSTD_DStream* zds)
 {
+    if (zds==NULL) return 0;   /* support sizeof on NULL */
     return sizeof(*zds) + ZSTD_sizeof_DCtx(zds->dctx) + ZSTD_sizeof_DDict(zds->ddict) + zds->inBuffSize + zds->outBuffSize;
 }
 
diff --git a/lib/zstd.h b/lib/zstd.h
index 985c6cd4b..93d8d212e 100644
--- a/lib/zstd.h
+++ b/lib/zstd.h
@@ -352,14 +352,18 @@ ZSTDLIB_API size_t ZSTD_estimateCCtxSize(ZSTD_compressionParameters cParams);
  *  Create a ZSTD compression context using external alloc and free functions */
 ZSTDLIB_API ZSTD_CCtx* ZSTD_createCCtx_advanced(ZSTD_customMem customMem);
 
+/*! ZSTD_sizeofCCtx() :
+ *  Gives the amount of memory used by a given ZSTD_CCtx */
+ZSTDLIB_API size_t ZSTD_sizeof_CCtx(const ZSTD_CCtx* cctx);
+
 /*! ZSTD_createCDict_advanced() :
  *  Create a ZSTD_CDict using external alloc and free, and customized compression parameters */
 ZSTDLIB_API ZSTD_CDict* ZSTD_createCDict_advanced(const void* dict, size_t dictSize,
                                                   ZSTD_parameters params, ZSTD_customMem customMem);
 
-/*! ZSTD_sizeofCCtx() :
- *  Gives the amount of memory used by a given ZSTD_CCtx */
-ZSTDLIB_API size_t ZSTD_sizeof_CCtx(const ZSTD_CCtx* cctx);
+/*! ZSTD_sizeof_CDict() :
+ *  Gives the amount of memory used by a given ZSTD_sizeof_CDict */
+ZSTDLIB_API size_t ZSTD_sizeof_CDict(const ZSTD_CDict* cdict);
 
 /*! ZSTD_getParams() :
 *   same as ZSTD_getCParams(), but @return a full `ZSTD_parameters` object instead of a `ZSTD_compressionParameters`.
@@ -399,7 +403,7 @@ ZSTDLIB_API size_t ZSTD_estimateDCtxSize(void);
  *  Create a ZSTD decompression context using external alloc and free functions */
 ZSTDLIB_API ZSTD_DCtx* ZSTD_createDCtx_advanced(ZSTD_customMem customMem);
 
-/*! ZSTD_sizeofDCtx() :
+/*! ZSTD_sizeof_DCtx() :
  *  Gives the amount of memory used by a given ZSTD_DCtx */
 ZSTDLIB_API size_t ZSTD_sizeof_DCtx(const ZSTD_DCtx* dctx);