diff --git a/src/tpm_library.c b/src/tpm_library.c
index 5dd8fa4e..20153b7b 100644
--- a/src/tpm_library.c
+++ b/src/tpm_library.c
@@ -636,6 +636,8 @@ TPM_RESULT CopyCachedState(enum TPMLIB_StateType st,
     *is_empty_buffer = (*buflen == BUFLEN_EMPTY_BUFFER);
 
     if (cached_blobs[st].buffer) {
+        assert(*buflen != BUFLEN_EMPTY_BUFFER);
+
         *buffer = malloc(*buflen);
         if (!*buffer) {
             TPMLIB_LogError("Could not allocate %u bytes.\n", *buflen);