Index: tests/natools-s_expressions-parsers-tests.adb
==================================================================
--- tests/natools-s_expressions-parsers-tests.adb
+++ tests/natools-s_expressions-parsers-tests.adb
@@ -115,10 +115,12 @@
    procedure All_Tests (Report : in out NT.Reporter'Class) is
    begin
       Canonical_Encoding (Report);
       Atom_Encodings (Report);
       Base64_Subexpression (Report);
+      Special_Subexpression (Report);
+      Nested_Subpexression (Report);
       Number_Prefixes (Report);
       Quoted_Escapes (Report);
    end All_Tests;
 
 
@@ -165,10 +167,24 @@
          Expected => To_Atom ("4:head((7:sublist)5:token)4:tail"));
    begin
       Test (Report);
    end Base64_Subexpression;
 
+
+   procedure Nested_Subpexression (Report : in out NT.Reporter'Class) is
+      procedure Test is new Blackbox_Test
+        (Name => "Nested base-64 subepxressions",
+         Source => To_Atom ("(5:begin"
+           & "{KG5lc3RlZCB7S0dSbFpYQWdjR0Y1Ykc5aFpDaz19KQ==}"
+           & "end)"),
+         Expected => To_Atom ("(5:begin"
+           & "(6:nested(4:deep7:payload))"
+           & "3:end)"));
+   begin
+      Test (Report);
+   end Nested_Subpexression;
+
 
    procedure Number_Prefixes (Report : in out NT.Reporter'Class) is
       procedure Test is new Blackbox_Test
         (Name => "Number prefixes",
          Source => To_Atom ("8:verbatim"
@@ -209,6 +225,22 @@
            & "(7:special2:\x1:"")"));
    begin
       Test (Report);
    end Quoted_Escapes;
 
+
+   procedure Special_Subexpression (Report : in out NT.Reporter'Class) is
+      procedure Test is new Blackbox_Test
+        (Name => "Special base-64 subexpression",
+         Source => To_Atom ("(begin "
+           & "{aGlkZGVuLWVuZCkoaGlkZGVuLWJlZ2lu}"
+           & " end)"
+           & "({MTY6b3ZlcmZsb3dpbmc=} atom)"),
+         Expected => To_Atom ("(5:begin"
+           & "10:hidden-end)(12:hidden-begin"
+           & "3:end)"
+           & "(16:overflowing atom)"));
+   begin
+      Test (Report);
+   end Special_Subexpression;
+
 end Natools.S_Expressions.Parsers.Tests;

Index: tests/natools-s_expressions-parsers-tests.ads
==================================================================
--- tests/natools-s_expressions-parsers-tests.ads
+++ tests/natools-s_expressions-parsers-tests.ads
@@ -29,9 +29,11 @@
    procedure All_Tests (Report : in out NT.Reporter'Class);
 
    procedure Atom_Encodings (Report : in out NT.Reporter'Class);
    procedure Base64_Subexpression (Report : in out NT.Reporter'Class);
    procedure Canonical_Encoding (Report : in out NT.Reporter'Class);
+   procedure Nested_Subpexression (Report : in out NT.Reporter'Class);
    procedure Number_Prefixes (Report : in out NT.Reporter'Class);
    procedure Quoted_Escapes (Report : in out NT.Reporter'Class);
+   procedure Special_Subexpression (Report : in out NT.Reporter'Class);
 
 end Natools.S_Expressions.Parsers.Tests;