diff --git a/index/gt/gtkada.toml b/index/gt/gtkada.toml
index 5913a126..f274d8d7 100644
--- a/index/gt/gtkada.toml
+++ b/index/gt/gtkada.toml
@@ -6,5 +6,6 @@ maintainers-logins = ["mosteo"]
 
 [[external]]
 kind = "system"
+available.'case(toolchain)'.user = false
    [external.origin.'case(distribution)']
    'debian|ubuntu' = ["libgtkada16.1.0-dev"]
diff --git a/index/nc/ncursesada.toml b/index/nc/ncursesada.toml
index b4916925..144ce0db 100644
--- a/index/nc/ncursesada.toml
+++ b/index/nc/ncursesada.toml
@@ -11,6 +11,8 @@ licenses = []
 
 [[external]]
 kind = "system"
+available.'case(toolchain)'.user = false
+
     [external.origin.'case(distribution)']
     'debian|ubuntu' = ["libncursesada6.1.20180127-dev",
                        "libncursesada5-dev",
diff --git a/index/pl/plplot.toml b/index/pl/plplot.toml
index ee9057cb..d4372f68 100644
--- a/index/pl/plplot.toml
+++ b/index/pl/plplot.toml
@@ -8,3 +8,4 @@ maintainers-logins = ["mosteo"]
 [[external]]
 kind = "system"
 origin = ["libplplot-ada-dev"]
+available.'case(toolchain)'.user = false