diff --git a/tests/Dockerfile-dind-certs b/tests/Dockerfile-dind-certs
index 7b819eb154..9d5c58fb2d 100644
--- a/tests/Dockerfile-dind-certs
+++ b/tests/Dockerfile-dind-certs
@@ -7,17 +7,46 @@ RUN mkdir /tmp/certs
 VOLUME /certs
 
 WORKDIR /tmp/certs
+
+# ---- CA (with proper v3_ca) ----
 RUN openssl genrsa -aes256 -passout pass:foobar -out ca-key.pem 4096
-RUN echo "[req]\nprompt=no\ndistinguished_name = req_distinguished_name\n[req_distinguished_name]\ncountryName=AU" > /tmp/config
-RUN openssl req -new -x509 -passin pass:foobar -config /tmp/config -days 365 -key ca-key.pem -sha256 -out ca.pem
-RUN openssl genrsa -out server-key.pem -passout pass:foobar 4096
+COPY <<'EOF' /tmp/ca.cnf
+[req]
+prompt = no
+distinguished_name = req_distinguished_name
+x509_extensions = v3_ca
+
+[req_distinguished_name]
+countryName = AU
+
+[v3_ca]
+basicConstraints = critical, CA:TRUE
+keyUsage = critical, keyCertSign, cRLSign
+subjectKeyIdentifier = hash
+authorityKeyIdentifier = keyid:always,issuer
+EOF
+RUN openssl req -new -x509 -passin pass:foobar -config /tmp/ca.cnf -days 365 -key ca-key.pem -sha256 -out ca.pem
+
+# ---- Server cert (SAN + KU/EKU) ----
+RUN openssl genrsa -out server-key.pem 4096
 RUN openssl req -subj "/CN=docker" -sha256 -new -key server-key.pem -out server.csr
-RUN echo subjectAltName = DNS:docker,DNS:localhost > extfile.cnf
-RUN openssl x509 -req -days 365 -passin pass:foobar -sha256 -in server.csr -CA ca.pem -CAkey ca-key.pem -CAcreateserial -out server-cert.pem -extfile extfile.cnf
+COPY <<'EOF' /tmp/server-ext.cnf
+basicConstraints = CA:FALSE
+keyUsage = critical, digitalSignature, keyEncipherment
+extendedKeyUsage = serverAuth
+subjectAltName = DNS:docker, DNS:localhost
+EOF
+RUN openssl x509 -req -days 365 -passin pass:foobar -sha256 -in server.csr -CA ca.pem -CAkey ca-key.pem -CAcreateserial -out server-cert.pem -extfile /tmp/server-ext.cnf
+
+# ---- Client cert (KU/EKU) ----
 RUN openssl genrsa -out key.pem 4096
 RUN openssl req -passin pass:foobar -subj '/CN=client' -new -key key.pem -out client.csr
-RUN echo extendedKeyUsage = clientAuth > extfile.cnf
-RUN openssl x509 -req -passin pass:foobar -days 365 -sha256 -in client.csr -CA ca.pem -CAkey ca-key.pem -CAcreateserial -out cert.pem -extfile extfile.cnf
+COPY <<'EOF' /tmp/client-ext.cnf
+basicConstraints = CA:FALSE
+keyUsage = critical, digitalSignature
+extendedKeyUsage = clientAuth
+EOF
+RUN openssl x509 -req -passin pass:foobar -days 365 -sha256 -in client.csr -CA ca.pem -CAkey ca-key.pem -CAcreateserial -out cert.pem -extfile /tmp/client-ext.cnf
 RUN chmod -v 0400 ca-key.pem key.pem server-key.pem
 RUN chmod -v 0444 ca.pem server-cert.pem cert.pem