diff --git a/CMakeLists.txt b/CMakeLists.txt
index 09b3048edef466dcddc5b043d1fc735a4cfefd4b..67b49f2ed4d91d9198b0c0425cb293be04e287f0 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -243,7 +243,10 @@ if(POETRY)
     list(REMOVE_DUPLICATES OGS_PYTHON_PACKAGES)
     list(SORT OGS_PYTHON_PACKAGES)
     string(SHA1 _ogs_python_packages_sha1 "${OGS_PYTHON_PACKAGES}")
-    if(NOT ${_ogs_python_packages_sha1} STREQUAL "${_OGS_PYTHON_PACKAGES_SHA1}")
+    list(LENGTH OGS_PYTHON_PACKAGES OGS_PYTHON_PACKAGES_LENGTH)
+    if(NOT ${_ogs_python_packages_sha1} STREQUAL "${_OGS_PYTHON_PACKAGES_SHA1}"
+       AND ${OGS_PYTHON_PACKAGES_LENGTH} GREATER 0
+    )
         execute_process(
             COMMAND ${CMD_COMMAND} poetry add ${OGS_PYTHON_PACKAGES}
             WORKING_DIRECTORY ${PROJECT_BINARY_DIR}
diff --git a/scripts/python/poetry.in.toml b/scripts/python/poetry.in.toml
index ab1033bd37224ee84b5862fb25f094db73809b74..253c85a9f38f81eccd4a00686ccad8abe1d98dca 100644
--- a/scripts/python/poetry.in.toml
+++ b/scripts/python/poetry.in.toml
@@ -1,2 +1,6 @@
 [virtualenvs]
 in-project = true
+
+# https://github.com/python-poetry/poetry/issues/4210
+[experimental]
+new-installer = false
diff --git a/web/data/versions.json b/web/data/versions.json
index e90c41de54e8bfc1054871c66aab3ad73a25d5cd..56c1b01e75dc81a871da74ebe3742f232b5c2998 100644
--- a/web/data/versions.json
+++ b/web/data/versions.json
@@ -39,8 +39,8 @@
       "https://github.com/joergbuchwald/ogs6py/archive/0f9e738e2ee469c8bde4204b2151238973417694.zip",
       "https://github.com/joergbuchwald/VTUinterface/archive/refs/heads/master.zip",
       "https://github.com/bilke/nb2hugo/archive/e27dc02df2be1ce19e4a6f52d197c2e2a6ca520c.zip",
-      "ipykernel",
-      "nbconvert"
+      "ipykernel==6.7.0",
+      "nbconvert==6.4.0"
     ]
   }
 }