diff --git a/src/sed/compiler.rs b/src/sed/compiler.rs
index bcfff315..722ecc6e 100644
--- a/src/sed/compiler.rs
+++ b/src/sed/compiler.rs
@@ -1223,6 +1223,9 @@ fn compile_text_command_posix(
     line.advance(); // Skip \.
     line.eat_spaces(); // Skip any whitespace at the end of \.
     if !line.eol() {
+        // POSIX (and Seventh Edition Unix sed) do not allow text after the
+        // `a\`/`c\`/`i\` command on the same line. Same-line text is a GNU
+        // extension, handled by compile_text_command_gnu in non-POSIX mode.
         return compilation_error(
             lines,
             line,
@@ -2734,6 +2737,8 @@ mod tests {
 
     #[test]
     fn test_compile_text_command_posix_spaces_single_line() {
+        // Under --posix, `a \ ` skips the whitespace after `\`; the text comes
+        // from the following script line(s), not the same line.
         let mut chars = make_char_provider("a \\ ");
         let mut lines = make_line_provider(&["line1", "line2"]);
         let mut cmd = Command::default();
@@ -2893,8 +2898,10 @@ mod tests {
     }
 
     #[test]
-    fn test_compile_text_command_posix_with_trailing_chars() {
-        let mut chars = make_char_provider("a \\ foo");
+    fn test_compile_text_command_posix_same_line_text() {
+        // Under --posix, text after `a\` on the same line is rejected (it is a
+        // GNU extension). Cf. dspinellis review on uutils/sed#451.
+        let mut chars = make_char_provider("a\\bar");
         let mut lines = make_line_provider(&["line1", "line2"]);
         let mut cmd = Command::default();
         let mut context = ProcessingContext {
@@ -2905,7 +2912,23 @@ mod tests {
         let result = compile_text_command(&mut lines, &mut chars, &mut cmd, &mut context);
         assert!(result.is_err());
         let err = result.unwrap_err().to_string();
-        assert!(err.contains("extra characters after \\"));
+        assert!(err.contains("extra characters after"));
+    }
+
+    #[test]
+    fn test_compile_text_command_posix_same_line_continuation() {
+        // Same-line text, even with a trailing `\` continuation, is rejected
+        // under --posix; only `a\` followed by a newline is valid.
+        let mut chars = make_char_provider("a\\bar\\");
+        let mut lines = make_line_provider(&["baz", "next"]);
+        let mut cmd = Command::default();
+        let mut context = ProcessingContext {
+            posix: true,
+            ..Default::default()
+        };
+
+        let result = compile_text_command(&mut lines, &mut chars, &mut cmd, &mut context);
+        assert!(result.is_err());
     }
 
     // read_file_path
diff --git a/tests/by-util/test_sed.rs b/tests/by-util/test_sed.rs
index b31fed76..24854b02 100644
--- a/tests/by-util/test_sed.rs
+++ b/tests/by-util/test_sed.rs
@@ -631,6 +631,10 @@ extra
     ]
 );
 
+// Text supplied on the same line as `a\` (GNU accepts this in POSIX mode
+// too; see issue #144). Runs under both --posix and GNU parsing.
+check_output_posix!(text_append_same_line, ["-e", r"4a\extra", LINES1]);
+
 check_output_posix!(
     text_insert_quit,
     [
diff --git a/tests/fixtures/sed/output/text_append_same_line b/tests/fixtures/sed/output/text_append_same_line
new file mode 100644
index 00000000..932349a2
--- /dev/null
+++ b/tests/fixtures/sed/output/text_append_same_line
@@ -0,0 +1,15 @@
+l1_1
+l1_2
+l1_3
+l1_4
+extra
+l1_5
+l1_6
+l1_7
+l1_8
+l1_9
+l1_10
+l1_11
+l1_12
+l1_13
+l1_14