diff --git a/scripts/nix-profile-daemon.sh.in b/scripts/nix-profile-daemon.sh.in
index 8cfd3149ee8..98adf46f768 100644
--- a/scripts/nix-profile-daemon.sh.in
+++ b/scripts/nix-profile-daemon.sh.in
@@ -1,6 +1,6 @@
 # Only execute this file once per shell.
 if [ -n "${__ETC_PROFILE_NIX_SOURCED:-}" ]; then return; fi
-__ETC_PROFILE_NIX_SOURCED=1
+export __ETC_PROFILE_NIX_SOURCED=1
 
 NIX_LINK=$HOME/.nix-profile
 if [ -n "${XDG_STATE_HOME-}" ]; then
@@ -60,5 +60,12 @@ else
   unset -f check_nix_profiles
 fi
 
-export PATH="$NIX_LINK/bin:@localstatedir@/nix/profiles/default/bin:$PATH"
+# only append once
+case ":$PATH:" in
+  *:"$NIX_LINK/bin:@localstatedir@/nix/profiles/default/bin":*)
+    ;;
+  *)
+    export PATH="$NIX_LINK/bin:@localstatedir@/nix/profiles/default/bin:$PATH"
+    ;;
+esac
 unset NIX_LINK
diff --git a/scripts/nix-profile.sh.in b/scripts/nix-profile.sh.in
index c4d60cf376a..b41437e536d 100644
--- a/scripts/nix-profile.sh.in
+++ b/scripts/nix-profile.sh.in
@@ -1,3 +1,7 @@
+# Only execute this file once per shell.
+if [ -n "${__ETC_PROFILE_NIX_SOURCED:-}" ]; then return; fi
+export __ETC_PROFILE_NIX_SOURCED=1
+
 if [ -n "$HOME" ] && [ -n "$USER" ]; then
 
     # Set up the per-user profile.
@@ -51,9 +55,24 @@ if [ -n "$HOME" ] && [ -n "$USER" ]; then
     # pick up `.nix-profile/share/man` because is it close to `.nix-profile/bin`
     # which is in the $PATH. For more info, run `manpath -d`.
     if [ -n "${MANPATH-}" ]; then
-        export MANPATH="$NIX_LINK/share/man:$MANPATH"
+        # only append once
+        case ":$MANPATH:" in
+          *:"$NIX_LINK/share/man":*)
+            ;;
+          *)
+            export MANPATH="$NIX_LINK/share/man:$MANPATH"
+            ;;
+        esac
     fi
 
-    export PATH="$NIX_LINK/bin:$PATH"
+    # only append once
+    case ":$PATH:" in
+      *:"$NIX_LINK/bin":*)
+        ;;
+      *)
+        export PATH="$NIX_LINK/bin:$PATH"
+        ;;
+    esac
+
     unset NIX_LINK NIX_LINK_NEW
 fi