diff --git a/crates/wit-component/src/printing.rs b/crates/wit-component/src/printing.rs
index 49e4058b09..13e03ce0c6 100644
--- a/crates/wit-component/src/printing.rs
+++ b/crates/wit-component/src/printing.rs
@@ -5,7 +5,7 @@ use std::mem;
 use wit_parser::*;
 
 // NB: keep in sync with `crates/wit-parser/src/ast/lex.rs`
-const PRINT_F32_F64_DEFAULT: bool = false;
+const PRINT_F32_F64_DEFAULT: bool = true;
 
 /// A utility for printing WebAssembly interface definitions to a string.
 pub struct WitPrinter {
diff --git a/crates/wit-parser/src/ast.rs b/crates/wit-parser/src/ast.rs
index 9d8d7716a1..8b49f2a760 100644
--- a/crates/wit-parser/src/ast.rs
+++ b/crates/wit-parser/src/ast.rs
@@ -1772,13 +1772,15 @@ impl SourceMap {
             bail!("{msg}")
         }
 
-        if let Some(sort) = err.downcast_ref::<toposort::Error>() {
-            let span = match sort {
-                toposort::Error::NonexistentDep { span, .. }
-                | toposort::Error::Cycle { span, .. } => *span,
-            };
-            let msg = self.highlight_err(span.start, Some(span.end), sort);
-            bail!("{msg}")
+        if let Some(sort) = err.downcast_mut::<toposort::Error>() {
+            if sort.highlighted().is_none() {
+                let span = match sort {
+                    toposort::Error::NonexistentDep { span, .. }
+                    | toposort::Error::Cycle { span, .. } => *span,
+                };
+                let highlighted = self.highlight_err(span.start, Some(span.end), &sort);
+                sort.set_highlighted(highlighted);
+            }
         }
 
         Err(err)
diff --git a/crates/wit-parser/src/ast/lex.rs b/crates/wit-parser/src/ast/lex.rs
index 76886d8547..a3a59cb945 100644
--- a/crates/wit-parser/src/ast/lex.rs
+++ b/crates/wit-parser/src/ast/lex.rs
@@ -116,7 +116,7 @@ pub enum Error {
 }
 
 // NB: keep in sync with `crates/wit-component/src/printing.rs`.
-const REQUIRE_F32_F64_BY_DEFAULT: bool = false;
+const REQUIRE_F32_F64_BY_DEFAULT: bool = true;
 
 impl<'a> Tokenizer<'a> {
     pub fn new(
diff --git a/crates/wit-parser/src/ast/resolve.rs b/crates/wit-parser/src/ast/resolve.rs
index 4a51aacce3..f32b502331 100644
--- a/crates/wit-parser/src/ast/resolve.rs
+++ b/crates/wit-parser/src/ast/resolve.rs
@@ -903,7 +903,7 @@ impl<'a> Resolver<'a> {
                 }
             }
         }
-        let order = toposort("type", &type_deps)?;
+        let order = toposort("type", &type_deps).map_err(attach_old_float_type_context)?;
         for ty in order {
             let def = match type_defs.swap_remove(&ty).unwrap() {
                 Some(def) => def,
@@ -922,7 +922,27 @@ impl<'a> Resolver<'a> {
             self.type_spans.push(def.name.span);
             self.define_interface_name(&def.name, TypeOrItem::Type(id))?;
         }
-        Ok(())
+        return Ok(());
+
+        fn attach_old_float_type_context(err: ast::toposort::Error) -> anyhow::Error {
+            let name = match &err {
+                ast::toposort::Error::NonexistentDep { name, .. } => name,
+                _ => return err.into(),
+            };
+            let new = match name.as_str() {
+                "float32" => "f32",
+                "float64" => "f64",
+                _ => return err.into(),
+            };
+
+            let context = format!(
+                "the `{name}` type has been renamed to `{new}` and is \
+                 no longer accepted, but the `WIT_REQUIRE_F32_F64=0` \
+                 environment variable can be used to temporarily \
+                 disable this error"
+            );
+            anyhow::Error::from(err).context(context)
+        }
     }
 
     fn resolve_use(&mut self, owner: TypeOwner, u: &ast::Use<'a>) -> Result<()> {
diff --git a/crates/wit-parser/src/ast/toposort.rs b/crates/wit-parser/src/ast/toposort.rs
index 0a43dc0325..4a4486c2d2 100644
--- a/crates/wit-parser/src/ast/toposort.rs
+++ b/crates/wit-parser/src/ast/toposort.rs
@@ -55,6 +55,7 @@ pub fn toposort<'a>(
                     span: edge.span,
                     name: edge.name.to_string(),
                     kind: kind.to_string(),
+                    highlighted: None,
                 })?;
             states[j].reverse_deps.push(i);
         }
@@ -115,6 +116,7 @@ pub fn toposort<'a>(
                 span: dep.span,
                 name: dep.name.to_string(),
                 kind: kind.to_string(),
+                highlighted: None,
             });
         }
     }
@@ -128,16 +130,38 @@ pub enum Error {
         span: Span,
         name: String,
         kind: String,
+        highlighted: Option<String>,
     },
     Cycle {
         span: Span,
         name: String,
         kind: String,
+        highlighted: Option<String>,
     },
 }
 
+impl Error {
+    pub(crate) fn highlighted(&self) -> Option<&str> {
+        match self {
+            Error::NonexistentDep { highlighted, .. } | Error::Cycle { highlighted, .. } => {
+                highlighted.as_deref()
+            }
+        }
+    }
+    pub(crate) fn set_highlighted(&mut self, string: String) {
+        match self {
+            Error::NonexistentDep { highlighted, .. } | Error::Cycle { highlighted, .. } => {
+                *highlighted = Some(string);
+            }
+        }
+    }
+}
+
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if let Some(s) = self.highlighted() {
+            return f.write_str(s);
+        }
         match self {
             Error::NonexistentDep { kind, name, .. } => {
                 write!(f, "{kind} `{name}` does not exist")
diff --git a/crates/wit-parser/tests/ui/parse-fail/old-float-types.wit b/crates/wit-parser/tests/ui/parse-fail/old-float-types.wit
new file mode 100644
index 0000000000..d74caac16a
--- /dev/null
+++ b/crates/wit-parser/tests/ui/parse-fail/old-float-types.wit
@@ -0,0 +1,5 @@
+package foo:bar;
+
+interface a {
+  type t1 = float32;
+}
diff --git a/crates/wit-parser/tests/ui/parse-fail/old-float-types.wit.result b/crates/wit-parser/tests/ui/parse-fail/old-float-types.wit.result
new file mode 100644
index 0000000000..e3a34fd62e
--- /dev/null
+++ b/crates/wit-parser/tests/ui/parse-fail/old-float-types.wit.result
@@ -0,0 +1,5 @@
+the `float32` type has been renamed to `f32` and is no longer accepted, but the `WIT_REQUIRE_F32_F64=0` environment variable can be used to temporarily disable this error: type `float32` does not exist
+     --> tests/ui/parse-fail/old-float-types.wit:4:13
+      |
+    4 |   type t1 = float32;
+      |             ^------
\ No newline at end of file