diff --git a/Dockerfile b/Dockerfile
index d191096..c19adad 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -20,17 +20,26 @@ RUN apt-get update && apt-get install -y \
     && rm -rf /var/lib/apt/lists/*
 
 # GNUnet (falls nicht schon systemweit neu genug)
-RUN if [ -n "${GNUNET_TARBALL_URL}" ]; then \
-      mkdir -p /src && cd /src && \
-      curl -L "${GNUNET_TARBALL_URL}" -o gnunet.tar.gz && \
-      tar xzf gnunet.tar.gz && \
-      cd gnunet-* && ./bootstrap && \
-      ./configure --prefix=/usr && make -j$(nproc) && make install; \
+RUN set -e; \
+    mkdir -p /src && cd /src; \
+    GNUNET_DIR=""; \
+    if [ -n "${GNUNET_TARBALL_URL}" ]; then \
+      echo "Fetching GNUnet tarball ${GNUNET_TARBALL_URL}"; \
+      curl -L "${GNUNET_TARBALL_URL}" -o gnunet.tar.gz; \
+      tar xzf gnunet.tar.gz; \
+      GNUNET_DIR="$(ls -d gnunet-* | head -1)"; \
+      if [ ! -f "${GNUNET_DIR}/doc/handbook/meson.build" ]; then \
+        echo "Tarball seems incomplete (doc/handbook/meson.build missing); falling back to git clone ${GNUNET_REF}"; \
+        rm -rf "${GNUNET_DIR}"; \
+        git clone --depth 1 --branch "${GNUNET_REF}" https://git.taler.net/gnunet.git gnunet; \
+        GNUNET_DIR="gnunet"; \
+      fi; \
     else \
-      git clone --depth 1 --branch "${GNUNET_REF}" https://git.taler.net/gnunet.git /src/gnunet && \
-      cd /src/gnunet && ./bootstrap && \
-      ./configure --prefix=/usr && make -j$(nproc) && make install; \
-    fi
+      git clone --depth 1 --branch "${GNUNET_REF}" https://git.taler.net/gnunet.git gnunet; \
+      GNUNET_DIR="gnunet"; \
+    fi; \
+    cd "${GNUNET_DIR}" && ./bootstrap && \
+    ./configure --prefix=/usr && make -j$(nproc) && make install
 
 # Taler Exchange + Merchant
 RUN git clone --depth 1 --branch "${EXCHANGE_REF}" https://git.taler.net/exchange.git /src/exchange && \