diff --git a/pkgs/stdenv/generic/setup.sh b/pkgs/stdenv/generic/setup.sh
index 9cc5cd89f3b7..dcccdaa50ae5 100644
--- a/pkgs/stdenv/generic/setup.sh
+++ b/pkgs/stdenv/generic/setup.sh
@@ -647,12 +647,12 @@ export NIX_BUILD_CORES
 
 
 # Prevent SSL libraries from using certificates in /etc/ssl, unless set explicitly.
-# Leave it in shells for convenience.
-if [ -z "${NIX_SSL_CERT_FILE:-}" ] && [ -z "${IN_NIX_SHELL:-}" ]; then
+# Leave it in impure shells for convenience.
+if [ -z "${NIX_SSL_CERT_FILE:-}" ] && [ "${IN_NIX_SHELL:-}" != "impure" ]; then
   export NIX_SSL_CERT_FILE=/no-cert-file.crt
 fi
 # Another variant left for compatibility.
-if [ -z "${SSL_CERT_FILE:-}" ] && [ -z "${IN_NIX_SHELL:-}" ]; then
+if [ -z "${SSL_CERT_FILE:-}" ] && [ "${IN_NIX_SHELL:-}" != "impure" ]; then
   export SSL_CERT_FILE=/no-cert-file.crt
 fi