diff --git a/.github/workflows/ci-macos.yml b/.github/workflows/ci-macos.yml
index db27c59b1..0b94b7272 100644
--- a/.github/workflows/ci-macos.yml
+++ b/.github/workflows/ci-macos.yml
@@ -15,7 +15,7 @@ jobs:
   build:
     name: CI on macOS
 
-    runs-on: macos-latest
+    runs-on: macos-10.15
 
     steps:
     - name: Check out repository
diff --git a/.github/workflows/ci-toolchain.yml b/.github/workflows/ci-toolchain.yml
index 013916396..c5f65e6f7 100644
--- a/.github/workflows/ci-toolchain.yml
+++ b/.github/workflows/ci-toolchain.yml
@@ -21,7 +21,7 @@ jobs:
     strategy:
       matrix:
         os: 
-          - macos-latest
+          - macos-10.15
           - ubuntu-latest
           - windows-latest
 
diff --git a/src/alire/alire-crate_configuration.adb b/src/alire/alire-crate_configuration.adb
index bd7ac85bd..1c633d1e9 100644
--- a/src/alire/alire-crate_configuration.adb
+++ b/src/alire/alire-crate_configuration.adb
@@ -185,7 +185,8 @@ package body Alire.Crate_Configuration is
            (Profile_Maps.Key (Cursor),
             (Name => +Builtin_Build_Profile.Name,
              Value => TOML.Create_String
-               (To_Lower_Case (Profile_Maps.Element (Cursor)'Img))));
+               (To_Lower_Case (Profile_Maps.Element (Cursor)'Img))),
+            Set_By => "Build profile map");
       end loop;
 
    end Make_Build_Profile_Map;
@@ -656,15 +657,15 @@ package body Alire.Crate_Configuration is
    -- Set_Value --
    ---------------
 
-   procedure Set_Value (This  : in out Global_Config;
-                        Crate : Crate_Name;
-                        Val   : Assignment)
+   procedure Set_Value (This   : in out Global_Config;
+                        Crate  : Crate_Name;
+                        Val    : Assignment;
+                        Set_By : String)
    is
       Val_Name_Lower : constant String := To_Lower_Case (+Val.Name);
       Crate_Str : constant String := +Crate;
       Name : constant Unbounded_String := (+Crate_Str) & "." & Val_Name_Lower;
    begin
-
       --  TODO check if setting configuration of a dependency
 
       if not This.Map.Contains (Name) then
@@ -683,14 +684,16 @@ package body Alire.Crate_Configuration is
                  "'" & " for type " & Image (Ref.Type_Def.Element));
          end if;
 
-         if Ref.Value /= No_TOML_Value and then Ref.Value /= Val.Value then
+         if Ref.Value.Is_Present and then not Ref.Value.Equals (Val.Value)
+         then
             Raise_Checked_Error
               ("Conflicting value for configuration variable '" &
-               (+Name) & "' from '" & (+Ref.Set_By) & "' and '"
-               & (+Crate) & "'.");
+               (+Name) & "' from '" & (+Ref.Set_By) & "' (" &
+                 Image (Ref.Value) & ") and '"
+               & Set_By & "' (" & Image (Val.Value) & ").");
          else
-            Ref.Value := Val.Value;
-            Ref.Set_By := +(+Crate);
+            Ref.Value  := Val.Value;
+            Ref.Set_By := +(Set_By);
          end if;
       end;
    end Set_Value;
@@ -716,7 +719,8 @@ package body Alire.Crate_Configuration is
               Config_Value_Assignment (Prop);
          begin
             for Elt of List.List loop
-               This.Set_Value (To_Name (+List.Crate), Elt);
+               This.Set_Value (To_Name (+List.Crate), Elt,
+                               Set_By => As_String (Crate));
             end loop;
          end;
       end loop;
diff --git a/src/alire/alire-crate_configuration.ads b/src/alire/alire-crate_configuration.ads
index 0302ddf0d..921dad252 100644
--- a/src/alire/alire-crate_configuration.ads
+++ b/src/alire/alire-crate_configuration.ads
@@ -84,9 +84,10 @@ private
                                Root  : in out Roots.Root;
                                Crate : Crate_Name);
 
-   procedure Set_Value (This  : in out Global_Config;
-                        Crate : Crate_Name;
-                        Val   : Assignment);
+   procedure Set_Value (This   : in out Global_Config;
+                        Crate  : Crate_Name;
+                        Val    : Assignment;
+                        Set_By : String);
 
    procedure Load_Settings (This  : in out Global_Config;
                             Root  : in out Roots.Root;
diff --git a/src/alire/alire-properties-configurations.adb b/src/alire/alire-properties-configurations.adb
index ce24ad62f..bb38a1417 100644
--- a/src/alire/alire-properties-configurations.adb
+++ b/src/alire/alire-properties-configurations.adb
@@ -129,7 +129,7 @@ package body Alire.Properties.Configurations is
          when TOML_String =>
             return Val.As_String;
          when TOML_Boolean =>
-            return Val.As_Boolean'Img;
+            return To_Lower_Case (Val.As_Boolean'Img);
          when TOML_Float =>
             return Image (Val.As_Float);
          when TOML_Integer =>
diff --git a/src/alire/alire-properties-configurations.ads b/src/alire/alire-properties-configurations.ads
index 6564a795b..2c643bb51 100644
--- a/src/alire/alire-properties-configurations.ads
+++ b/src/alire/alire-properties-configurations.ads
@@ -101,6 +101,9 @@ package Alire.Properties.Configurations with Preelaborate is
    function Typedef_From_Enum return Config_Type_Definition;
 
    function String_Typedef (Name : String) return Config_Type_Definition;
+
+   function Image (Val : TOML.TOML_Value) return String;
+
 private
 
    type Config_Entry is new Properties.Property with record
diff --git a/testsuite/tests/crate_config/value_conflict/my_index/index/he/hello_world/hello_world-0.1.0.toml b/testsuite/tests/crate_config/value_conflict/my_index/index/he/hello_world/hello_world-0.1.0.toml
new file mode 100644
index 000000000..4ba0c9350
--- /dev/null
+++ b/testsuite/tests/crate_config/value_conflict/my_index/index/he/hello_world/hello_world-0.1.0.toml
@@ -0,0 +1,14 @@
+description = "\"Hello, world!\" demonstration project"
+name = "hello_world"
+version = "0.1.0"
+licenses = "GPL-3.0-only"
+maintainers = ["example@example.com"]
+maintainers-logins = ["mylogin"]
+executables=['main']
+
+[origin]
+url = "file:."
+
+[[depends-on]]
+libcrate_config_b = "*"
+libcrate_config_c = "*"
diff --git a/testsuite/tests/crate_config/value_conflict/my_index/index/index.toml b/testsuite/tests/crate_config/value_conflict/my_index/index/index.toml
new file mode 100644
index 000000000..bad265e4f
--- /dev/null
+++ b/testsuite/tests/crate_config/value_conflict/my_index/index/index.toml
@@ -0,0 +1 @@
+version = "1.1"
diff --git a/testsuite/tests/crate_config/value_conflict/my_index/index/li/libcrate_config_a/libcrate_config_a-1.0.0.toml b/testsuite/tests/crate_config/value_conflict/my_index/index/li/libcrate_config_a/libcrate_config_a-1.0.0.toml
new file mode 100644
index 000000000..39d58201a
--- /dev/null
+++ b/testsuite/tests/crate_config/value_conflict/my_index/index/li/libcrate_config_a/libcrate_config_a-1.0.0.toml
@@ -0,0 +1,12 @@
+description = "crate config demonstration project"
+name = "libcrate_config_a"
+version = "1.0.0"
+licenses = "GPL-3.0-only"
+maintainers = ["example@example.com"]
+maintainers-logins = ["mylogin"]
+
+[origin]
+url = "file:."
+
+[configuration.variables]
+Var_Bool = {type="Boolean"}
diff --git a/testsuite/tests/crate_config/value_conflict/my_index/index/li/libcrate_config_b/libcrate_config_b-1.0.0.toml b/testsuite/tests/crate_config/value_conflict/my_index/index/li/libcrate_config_b/libcrate_config_b-1.0.0.toml
new file mode 100644
index 000000000..1277e7db8
--- /dev/null
+++ b/testsuite/tests/crate_config/value_conflict/my_index/index/li/libcrate_config_b/libcrate_config_b-1.0.0.toml
@@ -0,0 +1,15 @@
+description = "crate config demonstration project"
+name = "libcrate_config_b"
+version = "1.0.0"
+licenses = "GPL-3.0-only"
+maintainers = ["example@example.com"]
+maintainers-logins = ["mylogin"]
+
+[[depends-on]]
+libcrate_config_a = "*"
+
+[origin]
+url = "file:."
+
+[configuration.values]
+libcrate_config_a.Var_Bool = true
diff --git a/testsuite/tests/crate_config/value_conflict/my_index/index/li/libcrate_config_c/libcrate_config_c-1.0.0.toml b/testsuite/tests/crate_config/value_conflict/my_index/index/li/libcrate_config_c/libcrate_config_c-1.0.0.toml
new file mode 100644
index 000000000..10cfb3601
--- /dev/null
+++ b/testsuite/tests/crate_config/value_conflict/my_index/index/li/libcrate_config_c/libcrate_config_c-1.0.0.toml
@@ -0,0 +1,15 @@
+description = "crate config demonstration project"
+name = "libcrate_config_c"
+version = "1.0.0"
+licenses = "GPL-3.0-only"
+maintainers = ["example@example.com"]
+maintainers-logins = ["mylogin"]
+
+[[depends-on]]
+libcrate_config_a = "*"
+
+[origin]
+url = "file:."
+
+[configuration.values]
+libcrate_config_a.Var_Bool = false
diff --git a/testsuite/tests/crate_config/value_conflict/test.py b/testsuite/tests/crate_config/value_conflict/test.py
new file mode 100644
index 000000000..69ad4cc11
--- /dev/null
+++ b/testsuite/tests/crate_config/value_conflict/test.py
@@ -0,0 +1,24 @@
+"""
+Test that two crates setting the same config var to the different values is not
+ok.
+"""
+
+from drivers.alr import run_alr
+from drivers.asserts import assert_match
+
+import os
+import platform
+
+p = run_alr('get', 'hello_world', complain_on_error=False)
+assert p.status != 0, "alr should have errored"
+
+print(p.out)
+assert_match(".*\n"
+             "ERROR: Conflicting value for configuration variable"
+             " 'libcrate_config_a.var_bool'"
+             " from 'libcrate_config_b' \(true\)"
+             " and 'libcrate_config_c' \(false\).*"
+             ,
+             p.out)
+
+print('SUCCESS')
diff --git a/testsuite/tests/crate_config/value_conflict/test.yaml b/testsuite/tests/crate_config/value_conflict/test.yaml
new file mode 100644
index 000000000..0a859639c
--- /dev/null
+++ b/testsuite/tests/crate_config/value_conflict/test.yaml
@@ -0,0 +1,4 @@
+driver: python-script
+indexes:
+    my_index:
+        in_fixtures: false
diff --git a/testsuite/tests/crate_config/value_match/my_index/index/he/hello_world/hello_world-0.1.0.toml b/testsuite/tests/crate_config/value_match/my_index/index/he/hello_world/hello_world-0.1.0.toml
new file mode 100644
index 000000000..4ba0c9350
--- /dev/null
+++ b/testsuite/tests/crate_config/value_match/my_index/index/he/hello_world/hello_world-0.1.0.toml
@@ -0,0 +1,14 @@
+description = "\"Hello, world!\" demonstration project"
+name = "hello_world"
+version = "0.1.0"
+licenses = "GPL-3.0-only"
+maintainers = ["example@example.com"]
+maintainers-logins = ["mylogin"]
+executables=['main']
+
+[origin]
+url = "file:."
+
+[[depends-on]]
+libcrate_config_b = "*"
+libcrate_config_c = "*"
diff --git a/testsuite/tests/crate_config/value_match/my_index/index/index.toml b/testsuite/tests/crate_config/value_match/my_index/index/index.toml
new file mode 100644
index 000000000..bad265e4f
--- /dev/null
+++ b/testsuite/tests/crate_config/value_match/my_index/index/index.toml
@@ -0,0 +1 @@
+version = "1.1"
diff --git a/testsuite/tests/crate_config/value_match/my_index/index/li/libcrate_config_a/libcrate_config_a-1.0.0.toml b/testsuite/tests/crate_config/value_match/my_index/index/li/libcrate_config_a/libcrate_config_a-1.0.0.toml
new file mode 100644
index 000000000..f55a82d75
--- /dev/null
+++ b/testsuite/tests/crate_config/value_match/my_index/index/li/libcrate_config_a/libcrate_config_a-1.0.0.toml
@@ -0,0 +1,12 @@
+description = "crate config demonstration project"
+name = "libcrate_config_a"
+version = "1.0.0"
+licenses = "GPL-3.0-only"
+maintainers = ["example@example.com"]
+maintainers-logins = ["mylogin"]
+
+[origin]
+url = "file:."
+
+[configuration.variables]
+Var_Bool = {type="Boolean", default=true}
diff --git a/testsuite/tests/crate_config/value_match/my_index/index/li/libcrate_config_b/libcrate_config_b-1.0.0.toml b/testsuite/tests/crate_config/value_match/my_index/index/li/libcrate_config_b/libcrate_config_b-1.0.0.toml
new file mode 100644
index 000000000..feea80502
--- /dev/null
+++ b/testsuite/tests/crate_config/value_match/my_index/index/li/libcrate_config_b/libcrate_config_b-1.0.0.toml
@@ -0,0 +1,15 @@
+description = "crate config demonstration project"
+name = "libcrate_config_b"
+version = "1.0.0"
+licenses = "GPL-3.0-only"
+maintainers = ["example@example.com"]
+maintainers-logins = ["mylogin"]
+
+[[depends-on]]
+libcrate_config_a = "*"
+
+[origin]
+url = "file:."
+
+[configuration.values]
+libcrate_config_a.Var_Bool = false
diff --git a/testsuite/tests/crate_config/value_match/my_index/index/li/libcrate_config_c/libcrate_config_c-1.0.0.toml b/testsuite/tests/crate_config/value_match/my_index/index/li/libcrate_config_c/libcrate_config_c-1.0.0.toml
new file mode 100644
index 000000000..10cfb3601
--- /dev/null
+++ b/testsuite/tests/crate_config/value_match/my_index/index/li/libcrate_config_c/libcrate_config_c-1.0.0.toml
@@ -0,0 +1,15 @@
+description = "crate config demonstration project"
+name = "libcrate_config_c"
+version = "1.0.0"
+licenses = "GPL-3.0-only"
+maintainers = ["example@example.com"]
+maintainers-logins = ["mylogin"]
+
+[[depends-on]]
+libcrate_config_a = "*"
+
+[origin]
+url = "file:."
+
+[configuration.values]
+libcrate_config_a.Var_Bool = false
diff --git a/testsuite/tests/crate_config/value_match/test.py b/testsuite/tests/crate_config/value_match/test.py
new file mode 100644
index 000000000..8c1631142
--- /dev/null
+++ b/testsuite/tests/crate_config/value_match/test.py
@@ -0,0 +1,13 @@
+"""
+Test that two crates setting the same config var to the same value is ok.
+"""
+
+from drivers.alr import run_alr
+from drivers.asserts import assert_match
+
+import os
+import platform
+
+p = run_alr('get', 'hello_world')
+
+print('SUCCESS')
diff --git a/testsuite/tests/crate_config/value_match/test.yaml b/testsuite/tests/crate_config/value_match/test.yaml
new file mode 100644
index 000000000..0a859639c
--- /dev/null
+++ b/testsuite/tests/crate_config/value_match/test.yaml
@@ -0,0 +1,4 @@
+driver: python-script
+indexes:
+    my_index:
+        in_fixtures: false
diff --git a/testsuite/tests/show/jekyll/test.py b/testsuite/tests/show/jekyll/test.py
index cee9485f6..0f0aa78c6 100644
--- a/testsuite/tests/show/jekyll/test.py
+++ b/testsuite/tests/show/jekyll/test.py
@@ -29,8 +29,8 @@
       '{name: \'Var5\', type: \'Integer range -1 .. 1\', default: "0"},\n'
       '{name: \'Var6\', type: \'Real range -1.00000000000000E+00 .. 1.00000000000000E+00\', default: "0.00000000000000E+00"},\n'
       '{name: \'Var7\', type: \'Real range -inf .. +inf\', default: "0.00000000000000E+00"}]\n'
-      'configuration_values: [{crate: \'hello\', settings: [{name: \'Var1\', value: "TRUE"}]},\n'
-      '{crate: \'libhello\', settings: [{name: \'Var1\', value: "FALSE"}]}]\n'
+      'configuration_values: [{crate: \'hello\', settings: [{name: \'Var1\', value: "true"}]},\n'
+      '{crate: \'libhello\', settings: [{name: \'Var1\', value: "false"}]}]\n'
       '\n'
       '---\n'
       'This is an example of long description in a multi-line string.\n'