diff --git a/src/libexpr/primops/flake.cc b/src/libexpr/primops/flake.cc
index f068569a6..7cfb2038c 100644
--- a/src/libexpr/primops/flake.cc
+++ b/src/libexpr/primops/flake.cc
@@ -289,7 +289,7 @@ static std::tuple<FlakeId, std::map<FlakeId, Flake>> resolveFlake(EvalState & st
 
 #if 0
         if (evalSettings.pureEval && !flakeRef.isImmutable() && (!toplevel || !impureTopRef))
-            throw Error("mutable flake '%s' is not allowed in pure mode; use --no-pure-eval to disable", flakeRef.to_string());
+            throw Error("mutable flake '%s' is not allowed in pure mode; use --impure to disable", flakeRef.to_string());
 #endif
 
         auto flake = getFlake(state, flakeRef);
diff --git a/src/nix/installables.cc b/src/nix/installables.cc
index 6d3969e95..631a849cd 100644
--- a/src/nix/installables.cc
+++ b/src/nix/installables.cc
@@ -21,6 +21,13 @@ SourceExprCommand::SourceExprCommand()
         .label("file")
         .description("evaluate a set of attributes from FILE (deprecated)")
         .dest(&file);
+
+    mkFlag()
+        .longName("impure")
+        .description("allow access to mutable paths and repositories")
+        .handler([&](std::vector<std::string> ss) {
+            evalSettings.pureEval = false;
+        });
 }
 
 ref<EvalState> SourceExprCommand::getEvalState()
diff --git a/tests/fetchGit.sh b/tests/fetchGit.sh
index 301bf3022..51fd49e9f 100644
--- a/tests/fetchGit.sh
+++ b/tests/fetchGit.sh
@@ -26,11 +26,11 @@ git -C $repo commit -m 'Bla2' -a
 rev2=$(git -C $repo rev-parse HEAD)
 
 # Fetch the default branch.
-path=$(nix eval --no-pure-eval --raw "(builtins.fetchGit file://$repo).outPath")
+path=$(nix eval --impure --raw "(builtins.fetchGit file://$repo).outPath")
 [[ $(cat $path/hello) = world ]]
 
 # In pure eval mode, fetchGit without a revision should fail.
-[[ $(nix eval --no-pure-eval --raw "(builtins.readFile (fetchGit file://$repo + \"/hello\"))") = world ]]
+[[ $(nix eval --impure --raw "(builtins.readFile (fetchGit file://$repo + \"/hello\"))") = world ]]
 (! nix eval --raw "(builtins.readFile (fetchGit file://$repo + \"/hello\"))")
 
 # Fetch using an explicit revision hash.
@@ -42,14 +42,14 @@ path2=$(nix eval --raw "(builtins.fetchGit { url = file://$repo; rev = \"$rev2\"
 
 # Fetch again. This should be cached.
 mv $repo ${repo}-tmp
-path2=$(nix eval --no-pure-eval --raw "(builtins.fetchGit file://$repo).outPath")
+path2=$(nix eval --impure --raw "(builtins.fetchGit file://$repo).outPath")
 [[ $path = $path2 ]]
 
-[[ $(nix eval --no-pure-eval "(builtins.fetchGit file://$repo).revCount") = 2 ]]
-[[ $(nix eval --no-pure-eval --raw "(builtins.fetchGit file://$repo).rev") = $rev2 ]]
+[[ $(nix eval --impure "(builtins.fetchGit file://$repo).revCount") = 2 ]]
+[[ $(nix eval --impure --raw "(builtins.fetchGit file://$repo).rev") = $rev2 ]]
 
 # But with TTL 0, it should fail.
-(! nix eval --no-pure-eval --tarball-ttl 0 "(builtins.fetchGit file://$repo)" -vvvvv)
+(! nix eval --impure --tarball-ttl 0 "(builtins.fetchGit file://$repo)" -vvvvv)
 
 # Fetching with a explicit hash should succeed.
 path2=$(nix eval --tarball-ttl 0 --raw "(builtins.fetchGit { url = file://$repo; rev = \"$rev2\"; }).outPath")
@@ -61,7 +61,7 @@ path2=$(nix eval --tarball-ttl 0 --raw "(builtins.fetchGit { url = file://$repo;
 mv ${repo}-tmp $repo
 
 # Using a clean working tree should produce the same result.
-path2=$(nix eval --no-pure-eval --raw "(builtins.fetchGit $repo).outPath")
+path2=$(nix eval --impure --raw "(builtins.fetchGit $repo).outPath")
 [[ $path = $path2 ]]
 
 # Using an unclean tree should yield the tracked but uncommitted changes.
@@ -72,17 +72,17 @@ echo bar > $repo/dir2/bar
 git -C $repo add dir1/foo
 git -C $repo rm hello
 
-path2=$(nix eval --no-pure-eval --raw "(builtins.fetchGit $repo).outPath")
+path2=$(nix eval --impure --raw "(builtins.fetchGit $repo).outPath")
 [ ! -e $path2/hello ]
 [ ! -e $path2/bar ]
 [ ! -e $path2/dir2/bar ]
 [ ! -e $path2/.git ]
 [[ $(cat $path2/dir1/foo) = foo ]]
 
-[[ $(nix eval --no-pure-eval --raw "(builtins.fetchGit $repo).rev") = 0000000000000000000000000000000000000000 ]]
+[[ $(nix eval --impure --raw "(builtins.fetchGit $repo).rev") = 0000000000000000000000000000000000000000 ]]
 
 # ... unless we're using an explicit ref or rev.
-path3=$(nix eval --no-pure-eval --raw "(builtins.fetchGit { url = $repo; ref = \"master\"; }).outPath")
+path3=$(nix eval --impure --raw "(builtins.fetchGit { url = $repo; ref = \"master\"; }).outPath")
 [[ $path = $path3 ]]
 
 path3=$(nix eval --raw "(builtins.fetchGit { url = $repo; rev = \"$rev2\"; }).outPath")
@@ -91,7 +91,7 @@ path3=$(nix eval --raw "(builtins.fetchGit { url = $repo; rev = \"$rev2\"; }).ou
 # Committing should not affect the store path.
 git -C $repo commit -m 'Bla3' -a
 
-path4=$(nix eval --no-pure-eval --tarball-ttl 0 --raw "(builtins.fetchGit file://$repo).outPath")
+path4=$(nix eval --impure --tarball-ttl 0 --raw "(builtins.fetchGit file://$repo).outPath")
 [[ $path2 = $path4 ]]
 
 # tarball-ttl should be ignored if we specify a rev
@@ -102,29 +102,29 @@ rev3=$(git -C $repo rev-parse HEAD)
 nix eval --tarball-ttl 3600 "(builtins.fetchGit { url = $repo; rev = \"$rev3\"; })" >/dev/null
 
 # Update 'path' to reflect latest master
-path=$(nix eval --no-pure-eval --raw "(builtins.fetchGit file://$repo).outPath")
+path=$(nix eval --impure --raw "(builtins.fetchGit file://$repo).outPath")
 
 # Check behavior when non-master branch is used
 git -C $repo checkout $rev2 -b dev
 echo dev > $repo/hello
 
 # File URI uses 'master' unless specified otherwise
-path2=$(nix eval --no-pure-eval --raw "(builtins.fetchGit file://$repo).outPath")
+path2=$(nix eval --impure --raw "(builtins.fetchGit file://$repo).outPath")
 [[ $path = $path2 ]]
 
 # Using local path with branch other than 'master' should work when clean or dirty
-path3=$(nix eval --no-pure-eval --raw "(builtins.fetchGit $repo).outPath")
+path3=$(nix eval --impure --raw "(builtins.fetchGit $repo).outPath")
 # (check dirty-tree handling was used)
-[[ $(nix eval --no-pure-eval --raw "(builtins.fetchGit $repo).rev") = 0000000000000000000000000000000000000000 ]]
+[[ $(nix eval --impure --raw "(builtins.fetchGit $repo).rev") = 0000000000000000000000000000000000000000 ]]
 
 # Committing shouldn't change store path, or switch to using 'master'
 git -C $repo commit -m 'Bla5' -a
-path4=$(nix eval --no-pure-eval --raw "(builtins.fetchGit $repo).outPath")
+path4=$(nix eval --impure --raw "(builtins.fetchGit $repo).outPath")
 [[ $(cat $path4/hello) = dev ]]
 [[ $path3 = $path4 ]]
 
 # Confirm same as 'dev' branch
-path5=$(nix eval --no-pure-eval --raw "(builtins.fetchGit { url = $repo; ref = \"dev\"; }).outPath")
+path5=$(nix eval --impure --raw "(builtins.fetchGit { url = $repo; ref = \"dev\"; }).outPath")
 [[ $path3 = $path5 ]]
 
 
@@ -134,8 +134,8 @@ rm -rf $TEST_HOME/.cache/nix/gitv2
 # Try again, but without 'git' on PATH
 NIX=$(command -v nix)
 # This should fail
-(! PATH= $NIX eval --no-pure-eval --raw "(builtins.fetchGit { url = $repo; ref = \"dev\"; }).outPath" )
+(! PATH= $NIX eval --impure --raw "(builtins.fetchGit { url = $repo; ref = \"dev\"; }).outPath" )
 
 # Try again, with 'git' available.  This should work.
-path5=$(nix eval --no-pure-eval --raw "(builtins.fetchGit { url = $repo; ref = \"dev\"; }).outPath")
+path5=$(nix eval --impure --raw "(builtins.fetchGit { url = $repo; ref = \"dev\"; }).outPath")
 [[ $path3 = $path5 ]]
diff --git a/tests/fetchMercurial.sh b/tests/fetchMercurial.sh
index d0735a381..a0f792612 100644
--- a/tests/fetchMercurial.sh
+++ b/tests/fetchMercurial.sh
@@ -26,15 +26,15 @@ hg commit --cwd $repo -m 'Bla2'
 rev2=$(hg log --cwd $repo -r tip --template '{node}')
 
 # Fetch the default branch.
-path=$(nix eval --no-pure-eval --raw "(builtins.fetchMercurial file://$repo).outPath")
+path=$(nix eval --impure --raw "(builtins.fetchMercurial file://$repo).outPath")
 [[ $(cat $path/hello) = world ]]
 
 # In pure eval mode, fetchGit without a revision should fail.
-[[ $(nix eval --no-pure-eval --raw "(builtins.readFile (fetchMercurial file://$repo + \"/hello\"))") = world ]]
+[[ $(nix eval --impure --raw "(builtins.readFile (fetchMercurial file://$repo + \"/hello\"))") = world ]]
 (! nix eval --raw "(builtins.readFile (fetchMercurial file://$repo + \"/hello\"))")
 
 # Fetch using an explicit revision hash.
-path2=$(nix eval --no-pure-eval --raw "(builtins.fetchMercurial { url = file://$repo; rev = \"$rev2\"; }).outPath")
+path2=$(nix eval --impure --raw "(builtins.fetchMercurial { url = file://$repo; rev = \"$rev2\"; }).outPath")
 [[ $path = $path2 ]]
 
 # In pure eval mode, fetchGit with a revision should succeed.
@@ -42,15 +42,15 @@ path2=$(nix eval --no-pure-eval --raw "(builtins.fetchMercurial { url = file://$
 
 # Fetch again. This should be cached.
 mv $repo ${repo}-tmp
-path2=$(nix eval --no-pure-eval --raw "(builtins.fetchMercurial file://$repo).outPath")
+path2=$(nix eval --impure --raw "(builtins.fetchMercurial file://$repo).outPath")
 [[ $path = $path2 ]]
 
-[[ $(nix eval --no-pure-eval --raw "(builtins.fetchMercurial file://$repo).branch") = default ]]
-[[ $(nix eval --no-pure-eval "(builtins.fetchMercurial file://$repo).revCount") = 1 ]]
-[[ $(nix eval --no-pure-eval --raw "(builtins.fetchMercurial file://$repo).rev") = $rev2 ]]
+[[ $(nix eval --impure --raw "(builtins.fetchMercurial file://$repo).branch") = default ]]
+[[ $(nix eval --impure "(builtins.fetchMercurial file://$repo).revCount") = 1 ]]
+[[ $(nix eval --impure --raw "(builtins.fetchMercurial file://$repo).rev") = $rev2 ]]
 
 # But with TTL 0, it should fail.
-(! nix eval --no-pure-eval --tarball-ttl 0 "(builtins.fetchMercurial file://$repo)")
+(! nix eval --impure --tarball-ttl 0 "(builtins.fetchMercurial file://$repo)")
 
 # Fetching with a explicit hash should succeed.
 path2=$(nix eval --tarball-ttl 0 --raw "(builtins.fetchMercurial { url = file://$repo; rev = \"$rev2\"; }).outPath")
@@ -62,7 +62,7 @@ path2=$(nix eval --tarball-ttl 0 --raw "(builtins.fetchMercurial { url = file://
 mv ${repo}-tmp $repo
 
 # Using a clean working tree should produce the same result.
-path2=$(nix eval --no-pure-eval --raw "(builtins.fetchMercurial $repo).outPath")
+path2=$(nix eval --impure --raw "(builtins.fetchMercurial $repo).outPath")
 [[ $path = $path2 ]]
 
 # Using an unclean tree should yield the tracked but uncommitted changes.
@@ -73,14 +73,14 @@ echo bar > $repo/dir2/bar
 hg add --cwd $repo dir1/foo
 hg rm --cwd $repo hello
 
-path2=$(nix eval --no-pure-eval --raw "(builtins.fetchMercurial $repo).outPath")
+path2=$(nix eval --impure --raw "(builtins.fetchMercurial $repo).outPath")
 [ ! -e $path2/hello ]
 [ ! -e $path2/bar ]
 [ ! -e $path2/dir2/bar ]
 [ ! -e $path2/.hg ]
 [[ $(cat $path2/dir1/foo) = foo ]]
 
-[[ $(nix eval --no-pure-eval --raw "(builtins.fetchMercurial $repo).rev") = 0000000000000000000000000000000000000000 ]]
+[[ $(nix eval --impure --raw "(builtins.fetchMercurial $repo).rev") = 0000000000000000000000000000000000000000 ]]
 
 # ... unless we're using an explicit rev.
 path3=$(nix eval --raw "(builtins.fetchMercurial { url = $repo; rev = \"default\"; }).outPath")
@@ -89,5 +89,5 @@ path3=$(nix eval --raw "(builtins.fetchMercurial { url = $repo; rev = \"default\
 # Committing should not affect the store path.
 hg commit --cwd $repo -m 'Bla3'
 
-path4=$(nix eval --no-pure-eval --tarball-ttl 0 --raw "(builtins.fetchMercurial file://$repo).outPath")
+path4=$(nix eval --impure --tarball-ttl 0 --raw "(builtins.fetchMercurial file://$repo).outPath")
 [[ $path2 = $path4 ]]
diff --git a/tests/pure-eval.sh b/tests/pure-eval.sh
index 307942940..6e2c6962d 100644
--- a/tests/pure-eval.sh
+++ b/tests/pure-eval.sh
@@ -4,7 +4,7 @@ clearStore
 
 nix eval '(assert 1 + 2 == 3; true)'
 
-[[ $(nix eval --no-pure-eval '(builtins.readFile ./pure-eval.sh)') =~ clearStore ]]
+[[ $(nix eval --impure '(builtins.readFile ./pure-eval.sh)') =~ clearStore ]]
 
 (! nix eval '(builtins.readFile ./pure-eval.sh)')
 
@@ -13,6 +13,6 @@ nix eval '(assert 1 + 2 == 3; true)'
 
 (! nix-instantiate --pure-eval ./simple.nix)
 
-[[ $(nix eval --no-pure-eval "((import (builtins.fetchurl { url = file://$(pwd)/pure-eval.nix; })).x)") == 123 ]]
+[[ $(nix eval --impure "((import (builtins.fetchurl { url = file://$(pwd)/pure-eval.nix; })).x)") == 123 ]]
 (! nix eval "((import (builtins.fetchurl { url = file://$(pwd)/pure-eval.nix; })).x)")
 nix eval "((import (builtins.fetchurl { url = file://$(pwd)/pure-eval.nix; sha256 = \"$(nix hash-file pure-eval.nix --type sha256)\"; })).x)"
diff --git a/tests/restricted.sh b/tests/restricted.sh
index 68913cd36..e660de127 100644
--- a/tests/restricted.sh
+++ b/tests/restricted.sh
@@ -17,18 +17,18 @@ nix-instantiate --restrict-eval --eval -E 'builtins.readDir ../src/nix-channel'
 (! nix-instantiate --restrict-eval --eval -E 'let __nixPath = [ { prefix = "foo"; path = ./.; } ]; in <foo>')
 nix-instantiate --restrict-eval --eval -E 'let __nixPath = [ { prefix = "foo"; path = ./.; } ]; in <foo>' -I src=.
 
-p=$(nix eval --raw "(builtins.fetchurl file://$(pwd)/restricted.sh)" --no-pure-eval --restrict-eval --allowed-uris "file://$(pwd)")
+p=$(nix eval --raw "(builtins.fetchurl file://$(pwd)/restricted.sh)" --impure --restrict-eval --allowed-uris "file://$(pwd)")
 cmp $p restricted.sh
 
-(! nix eval --raw "(builtins.fetchurl file://$(pwd)/restricted.sh)" --no-pure-eval --restrict-eval)
+(! nix eval --raw "(builtins.fetchurl file://$(pwd)/restricted.sh)" --impure --restrict-eval)
 
-(! nix eval --raw "(builtins.fetchurl file://$(pwd)/restricted.sh)" --no-pure-eval --restrict-eval --allowed-uris "file://$(pwd)/restricted.sh/")
+(! nix eval --raw "(builtins.fetchurl file://$(pwd)/restricted.sh)" --impure --restrict-eval --allowed-uris "file://$(pwd)/restricted.sh/")
 
-nix eval --raw "(builtins.fetchurl file://$(pwd)/restricted.sh)" --no-pure-eval --restrict-eval --allowed-uris "file://$(pwd)/restricted.sh"
+nix eval --raw "(builtins.fetchurl file://$(pwd)/restricted.sh)" --impure --restrict-eval --allowed-uris "file://$(pwd)/restricted.sh"
 
-(! nix eval --raw "(builtins.fetchurl https://github.com/NixOS/patchelf/archive/master.tar.gz)" --no-pure-eval --restrict-eval)
-(! nix eval --raw "(builtins.fetchTarball https://github.com/NixOS/patchelf/archive/master.tar.gz)" --no-pure-eval --restrict-eval)
-(! nix eval --raw "(fetchGit git://github.com/NixOS/patchelf.git)" --no-pure-eval --restrict-eval)
+(! nix eval --raw "(builtins.fetchurl https://github.com/NixOS/patchelf/archive/master.tar.gz)" --impure --restrict-eval)
+(! nix eval --raw "(builtins.fetchTarball https://github.com/NixOS/patchelf/archive/master.tar.gz)" --impure --restrict-eval)
+(! nix eval --raw "(fetchGit git://github.com/NixOS/patchelf.git)" --impure --restrict-eval)
 
 ln -sfn $(pwd)/restricted.nix $TEST_ROOT/restricted.nix
 [[ $(nix-instantiate --eval $TEST_ROOT/restricted.nix) == 3 ]]
@@ -37,7 +37,7 @@ ln -sfn $(pwd)/restricted.nix $TEST_ROOT/restricted.nix
 (! nix-instantiate --eval --restrict-eval $TEST_ROOT/restricted.nix -I .)
 nix-instantiate --eval --restrict-eval $TEST_ROOT/restricted.nix -I $TEST_ROOT -I .
 
-[[ $(nix eval --raw --no-pure-eval --restrict-eval -I . '(builtins.readFile "${import ./simple.nix}/hello")') == 'Hello World!' ]]
+[[ $(nix eval --raw --impure --restrict-eval -I . '(builtins.readFile "${import ./simple.nix}/hello")') == 'Hello World!' ]]
 
 # Check whether we can leak symlink information through directory traversal.
 traverseDir="$(pwd)/restricted-traverse-me"