diff --git a/NUCLEIC_FORK.md b/NUCLEIC_FORK.md
index 4bd5d84..78d88bc 100644
--- a/NUCLEIC_FORK.md
+++ b/NUCLEIC_FORK.md
@@ -11,7 +11,16 @@ Every fork change is marked with a `// nash:` comment. Current patches:
 | --- | --- |
 | `brush-shell/src/productinfo.rs` | `PRODUCT_NAME` → `nash`; display string identifies the fork |
 | `brush-shell/src/args.rs` | usage/version strings rebranded |
-| `brush-core/src/expansion.rs` | corpus divergence D1: added `ExpansionPiece::LiteralText` — literal unquoted text is never field-split (bash splits only expansion results) but keeps glob characters active. Upstream candidate. |
+| `brush-core/src/expansion.rs` | corpus divergence D1: added `ExpansionPiece::LiteralText` — literal unquoted text is never field-split (bash splits only expansion results) but keeps glob characters active. Parameter-expansion substitutions (`${v:-word}` etc.) convert back to splittable at the expansion boundary; `ExpanderOptions.field_split_literal_text` lets data-string callers opt in. Upstream candidate. |
+| `brush-core/src/completion.rs` | `compgen -W` word list opts into `field_split_literal_text` (the -W string is data) |
+| `brush-shell/tests/cases/compat/ifs.yaml` | removed `known_failure` from 3 IFS tests the D1 fix repairs |
+
+Verification (this container): brush compat suite `2067 ran: 1684 succeeded, 6
+failed, 377 known to fail, 38 skipped` — the 6 failures are identical to a
+pristine `brush-shell-v0.4.0` baseline run (environmental: ANSI-C quote and
+`echo -e` oracle differences, syntax-error formatting, missing `hexdump`), i.e.
+zero fork-caused regressions; +3 successes vs baseline are the repaired IFS
+tests. nash corpus: 94/94.
 
 Planned (M1, per docs/NASH.md §4.2): `brush-core` `Gate` trait (verdict-shaped
 observation hooks) — the only substantial divergence from upstream.
diff --git a/brush-core/src/completion.rs b/brush-core/src/completion.rs
index 9884a8c..de75a53 100644
--- a/brush-core/src/completion.rs
+++ b/brush-core/src/completion.rs
@@ -308,6 +308,8 @@ impl Spec {
             // and field splitting but NOT pathname expansion (globbing).
             let options = crate::expansion::ExpanderOptions {
                 pathname_expand: false,
+                // nash: the -W string is data — its literal text is split too.
+                field_split_literal_text: true,
                 ..Default::default()
             };
             let words = crate::expansion::full_expand_and_split_word_with_options(
diff --git a/brush-core/src/expansion.rs b/brush-core/src/expansion.rs
index c8dfe04..d6a7385 100644
--- a/brush-core/src/expansion.rs
+++ b/brush-core/src/expansion.rs
@@ -37,6 +37,11 @@ pub(crate) struct ExpanderOptions {
     /// Whether to perform pathname expansion (globbing). If disabled, glob patterns
     /// are returned as literal strings.
     pub pathname_expand: bool,
+    // nash: whether literal (unquoted, non-expansion) text is also subject to
+    // field splitting. Off by default per POSIX/bash (only expansion results
+    // split); enabled by callers whose input string is *data*, e.g. the
+    // `compgen -W` word list.
+    pub field_split_literal_text: bool,
 }
 
 impl Default for ExpanderOptions {
@@ -46,6 +51,7 @@ impl Default for ExpanderOptions {
             brace_expand: true,
             execute_command_substitutions: true,
             pathname_expand: true,
+            field_split_literal_text: false,
         }
     }
 }
@@ -333,6 +339,15 @@ impl ExpansionPiece {
             Self::LiteralText(s) => Self::Unsplittable(s),
         }
     }
+
+    // nash: opt literal text into field splitting (see
+    // `ExpanderOptions::field_split_literal_text`). Quoted pieces stay intact.
+    fn make_literal_splittable(self) -> Self {
+        match self {
+            Self::LiteralText(s) => Self::Splittable(s),
+            other => other,
+        }
+    }
 }
 
 enum ParameterState {
@@ -532,6 +547,8 @@ struct WordExpander<'a, SE: extensions::ShellExtensions> {
     in_double_quotes: bool,
     /// Whether to use heredoc expansion semantics (literal quotes, no brace expansion).
     heredoc_mode: bool,
+    // nash: see `ExpanderOptions::field_split_literal_text`.
+    field_split_literal_text: bool,
 }
 
 impl<'a, SE: extensions::ShellExtensions> WordExpander<'a, SE> {
@@ -547,6 +564,7 @@ impl<'a, SE: extensions::ShellExtensions> WordExpander<'a, SE> {
             disable_pathname_expansion: false,
             in_double_quotes: false,
             heredoc_mode: false,
+            field_split_literal_text: false,
         }
     }
 
@@ -572,6 +590,7 @@ impl<'a, SE: extensions::ShellExtensions> WordExpander<'a, SE> {
             disable_pathname_expansion: !options.pathname_expand,
             in_double_quotes: false,
             heredoc_mode: false,
+            field_split_literal_text: options.field_split_literal_text,
         }
     }
 
@@ -802,6 +821,13 @@ impl<'a, SE: extensions::ShellExtensions> WordExpander<'a, SE> {
         // Go through the fields we have so far.
         for existing_field in expansion.fields {
             for piece in existing_field.0 {
+                // nash: callers whose input is data (e.g. compgen -W) opt
+                // literal text into splitting.
+                let piece = if self.field_split_literal_text {
+                    piece.make_literal_splittable()
+                } else {
+                    piece
+                };
                 match piece {
                     // nash: literal text is never field-split (only expansion
                     // results are), but stays a distinct piece so its glob
@@ -937,7 +963,19 @@ impl<'a, SE: extensions::ShellExtensions> WordExpander<'a, SE> {
                 ExpansionPiece::Unsplittable(self.expand_tilde_expression(&tilde_expr)?),
             ),
             brush_parser::word::WordPiece::ParameterExpansion(p) => {
-                self.expand_parameter_expr(p).await?
+                // nash: whatever a parameter expansion substitutes (including
+                // literal text from ${v:-default} / ${v:+alt} words) is an
+                // expansion *result*, so it is subject to field splitting.
+                // Quoted pieces inside remain Unsplittable.
+                let mut expansion = self.expand_parameter_expr(p).await?;
+                for field in &mut expansion.fields {
+                    for piece in &mut field.0 {
+                        if let ExpansionPiece::LiteralText(s) = piece {
+                            *piece = ExpansionPiece::Splittable(std::mem::take(s));
+                        }
+                    }
+                }
+                expansion
             }
             brush_parser::word::WordPiece::BackquotedCommandSubstitution(s)
             | brush_parser::word::WordPiece::CommandSubstitution(s) => {
diff --git a/brush-shell/tests/cases/compat/ifs.yaml b/brush-shell/tests/cases/compat/ifs.yaml
index 7b04241..64f6fb9 100644
--- a/brush-shell/tests/cases/compat/ifs.yaml
+++ b/brush-shell/tests/cases/compat/ifs.yaml
@@ -219,7 +219,7 @@ cases:
       echo "After: [$IFS]"
 
   - name: "IFS does not affect for loop literal words"
-    known_failure: true
+    # nash: fixed by ExpansionPiece::LiteralText (literal words are not field-split)
     stdin: |
       IFS=':'
       for word in a:b:c; do
@@ -249,7 +249,7 @@ cases:
       echo "Quoted: $var"
 
   - name: "IFS with partially quoted expansion"
-    known_failure: true
+    # nash: fixed by ExpansionPiece::LiteralText (literal words are not field-split)
     stdin: |
       IFS=':'
       var="a:b:c"
@@ -309,7 +309,7 @@ cases:
       echo "[$1]"
 
   - name: "IFS with glob pattern literal"
-    known_failure: true
+    # nash: fixed by ExpansionPiece::LiteralText (literal words are not field-split)
     stdin: |
       IFS=':'
       # Glob patterns as literals shouldn't split