diff --git a/mesonbuild/interpreter/interpreter.py b/mesonbuild/interpreter/interpreter.py
index 778a4d601..4191bee33 100644
--- a/mesonbuild/interpreter/interpreter.py
+++ b/mesonbuild/interpreter/interpreter.py
@@ -2583,8 +2583,9 @@ class Interpreter(InterpreterBase, HoldableObject):
         for a in incdir_strings:
             if a.startswith(src_root):
                 raise InvalidArguments(textwrap.dedent('''\
-                    Tried to form an absolute path to a source dir.
-                    You should not do that but use relative paths instead.
+                    Tried to form an absolute path to a dir in the source tree.
+                    You should not do that but use relative paths instead, for
+                    directories that are part of your project.
 
                     To get include path to any directory relative to the current dir do
 
@@ -2599,6 +2600,10 @@ class Interpreter(InterpreterBase, HoldableObject):
                     put in the include directories by default so you only need to do
                     include_directories('.') if you intend to use the result in a
                     different subdirectory.
+
+                    Note that this error message can also be triggered by
+                    external dependencies being installed within your source
+                    tree - it's not recommended to do this.
                     '''))
             else:
                 try:
diff --git a/test cases/failing/44 abspath to srcdir/test.json b/test cases/failing/44 abspath to srcdir/test.json
index 2cc298045..c64ecfbd6 100644
--- a/test cases/failing/44 abspath to srcdir/test.json	
+++ b/test cases/failing/44 abspath to srcdir/test.json	
@@ -1,7 +1,7 @@
 {
   "stdout": [
     {
-      "line": "test cases/failing/44 abspath to srcdir/meson.build:3:0: ERROR: Tried to form an absolute path to a source dir."
+      "line": "test cases/failing/44 abspath to srcdir/meson.build:3:0: ERROR: Tried to form an absolute path to a dir in the source tree."
     }
   ]
 }