diff --git a/library/lms.c b/library/lms.c
index 876deeb..ccbcd8b 100644
--- a/library/lms.c
+++ b/library/lms.c
@@ -603,7 +603,9 @@
         goto exit;
     }
 
-    ctx->ots_private_keys = mbedtls_calloc( MERKLE_TREE_LEAF_NODE_AM(ctx->params.type),
+    /* Requires a cast to size_t to avoid an implicit cast warning on certain
+     * platforms (particularly Windows) */
+    ctx->ots_private_keys = mbedtls_calloc( ( size_t )MERKLE_TREE_LEAF_NODE_AM(ctx->params.type),
                                             sizeof( *ctx->ots_private_keys ) );
     if( ctx->ots_private_keys == NULL )
     {
@@ -611,7 +613,9 @@
         goto exit;
     }
 
-    ctx->ots_public_keys = mbedtls_calloc( MERKLE_TREE_LEAF_NODE_AM(ctx->params.type),
+    /* Requires a cast to size_t to avoid an implicit cast warning on certain
+     * platforms (particularly Windows) */
+    ctx->ots_public_keys = mbedtls_calloc( ( size_t )MERKLE_TREE_LEAF_NODE_AM(ctx->params.type),
                                            sizeof( *ctx->ots_public_keys ) );
     if( ctx->ots_public_keys == NULL )
     {