diff --git a/lib/compress/zstd_compress.c b/lib/compress/zstd_compress.c
index a14c929ba..b56ce07d5 100644
--- a/lib/compress/zstd_compress.c
+++ b/lib/compress/zstd_compress.c
@@ -88,6 +88,7 @@ size_t ZSTD_rust_nextInputSizeHint(int inBufferMode,
                                    size_t inBuffPos);
 size_t ZSTD_rust_CStreamInSize(void);
 size_t ZSTD_rust_CStreamOutSize(void);
+size_t ZSTD_rust_sizeofCDict(size_t objectSize, size_t workspaceSize);
 size_t ZSTD_rust_sizeofLocalDict(int dictBufferPresent, size_t dictSize,
                                  size_t cdictSize);
 size_t ZSTD_rust_sizeofCCtx(size_t objectSize, size_t workspaceSize,
@@ -4000,11 +4001,13 @@ size_t ZSTD_estimateCDictSize(size_t dictSize, int compressionLevel)
 
 size_t ZSTD_sizeof_CDict(const ZSTD_CDict* cdict)
 {
+    size_t objectSize, workspaceSize;
     if (cdict==NULL) return 0;   /* support sizeof on NULL */
     DEBUGLOG(5, "sizeof(*cdict) : %u", (unsigned)sizeof(*cdict));
     /* cdict may be in the workspace */
-    return (cdict->workspace.workspace == cdict ? 0 : sizeof(*cdict))
-        + ZSTD_cwksp_sizeof(&cdict->workspace);
+    objectSize = cdict->workspace.workspace == cdict ? 0 : sizeof(*cdict);
+    workspaceSize = ZSTD_cwksp_sizeof(&cdict->workspace);
+    return ZSTD_rust_sizeofCDict(objectSize, workspaceSize);
 }
 
 static size_t ZSTD_initCDict_internal(
diff --git a/rust/src/zstd_compress.rs b/rust/src/zstd_compress.rs
index b25c631ed..47a840ca2 100644
--- a/rust/src/zstd_compress.rs
+++ b/rust/src/zstd_compress.rs
@@ -485,6 +485,18 @@ pub extern "C" fn ZSTD_rust_sizeofLocalDict(
     sizeof_local_dict(dict_buffer_present, dict_size, cdict_size)
 }
 
+#[inline]
+fn sizeof_cdict(object_size: usize, workspace_size: usize) -> usize {
+    object_size.wrapping_add(workspace_size)
+}
+
+/// Aggregate C-owned dictionary size components with C `size_t` wrapping
+/// semantics.
+#[no_mangle]
+pub extern "C" fn ZSTD_rust_sizeofCDict(objectSize: usize, workspaceSize: usize) -> usize {
+    sizeof_cdict(objectSize, workspaceSize)
+}
+
 #[inline]
 fn sizeof_cctx(
     object_size: usize,
@@ -1678,6 +1690,24 @@ mod tests {
         assert_eq!(sizeof_local_dict(0, usize::MAX, usize::MAX), usize::MAX);
     }
 
+    #[test]
+    fn sizeof_cdict_handles_zero_components() {
+        assert_eq!(sizeof_cdict(0, 0), 0);
+        assert_eq!(ZSTD_rust_sizeofCDict(0, 0), 0);
+    }
+
+    #[test]
+    fn sizeof_cdict_adds_components_in_order() {
+        assert_eq!(sizeof_cdict(17, 25), 42);
+        assert_eq!(ZSTD_rust_sizeofCDict(17, 25), 42);
+    }
+
+    #[test]
+    fn sizeof_cdict_wraps_like_c_size_t_addition() {
+        assert_eq!(sizeof_cdict(usize::MAX, 1), 0);
+        assert_eq!(ZSTD_rust_sizeofCDict(usize::MAX, 1), 0);
+    }
+
     #[test]
     fn sizeof_cctx_handles_zero_components() {
         assert_eq!(sizeof_cctx(0, 0, 0, 0), 0);