diff --git a/crates/fuzzing/src/oracles/engine.rs b/crates/fuzzing/src/oracles/engine.rs
index 5c7cf69c547a..887f8382b36c 100644
--- a/crates/fuzzing/src/oracles/engine.rs
+++ b/crates/fuzzing/src/oracles/engine.rs
@@ -93,14 +93,17 @@ pub fn setup_engine_runtimes() {
 /// Build a list of allowed values from the given `defaults` using the
 /// `env_list`.
 ///
+/// The entries in `defaults` are preserved, in order, and are replaced with
+/// `None` in the returned list if they are disabled.
+///
 /// ```
 /// # use wasmtime_fuzzing::oracles::engine::build_allowed_env_list;
 /// // Passing no `env_list` returns the defaults:
-/// assert_eq!(build_allowed_env_list(None, &["a"]), vec!["a"]);
+/// assert_eq!(build_allowed_env_list(None, &["a"]), vec![Some("a")]);
 /// // We can build up a subset of the defaults:
-/// assert_eq!(build_allowed_env_list(Some(vec!["b".to_string()]), &["a","b"]), vec!["b"]);
+/// assert_eq!(build_allowed_env_list(Some(vec!["b".to_string()]), &["a","b"]), vec![None, Some("b")]);
 /// // Alternately we can subtract from the defaults:
-/// assert_eq!(build_allowed_env_list(Some(vec!["-a".to_string()]), &["a","b"]), vec!["b"]);
+/// assert_eq!(build_allowed_env_list(Some(vec!["-a".to_string()]), &["a","b"]), vec![None, Some("b")]);
 /// ```
 /// ```should_panic
 /// # use wasmtime_fuzzing::oracles::engine::build_allowed_env_list;
@@ -116,7 +119,7 @@ pub fn setup_engine_runtimes() {
 pub fn build_allowed_env_list<'a>(
     env_list: Option<Vec<String>>,
     defaults: &[&'a str],
-) -> Vec<&'a str> {
+) -> Vec<Option<&'a str>> {
     if let Some(configured) = &env_list {
         // Check that the names are either all additions or all subtractions.
         let subtract_from_defaults = configured.iter().all(|c| c.starts_with("-"));
@@ -141,12 +144,14 @@ pub fn build_allowed_env_list<'a>(
         for &d in defaults {
             let mentioned = configured.iter().any(|c| &c[start..] == d);
             if (add_from_defaults && mentioned) || (subtract_from_defaults && !mentioned) {
-                allowed.push(d);
+                allowed.push(Some(d));
+            } else {
+                allowed.push(None);
             }
         }
         allowed
     } else {
-        defaults.to_vec()
+        defaults.iter().copied().map(Some).collect()
     }
 }
 
diff --git a/fuzz/fuzz_targets/differential.rs b/fuzz/fuzz_targets/differential.rs
index 802c8edeb9e8..5cc3fb4b4011 100644
--- a/fuzz/fuzz_targets/differential.rs
+++ b/fuzz/fuzz_targets/differential.rs
@@ -22,8 +22,8 @@ static SETUP: Once = Once::new();
 // - ALLOWED_ENGINES=wasmi,spec cargo +nightly fuzz run ...
 // - ALLOWED_ENGINES=-v8 cargo +nightly fuzz run ...
 // - ALLOWED_MODULES=single-inst cargo +nightly fuzz run ...
-static ALLOWED_ENGINES: Mutex<Vec<&str>> = Mutex::new(vec![]);
-static ALLOWED_MODULES: Mutex<Vec<&str>> = Mutex::new(vec![]);
+static ALLOWED_ENGINES: Mutex<Vec<Option<&str>>> = Mutex::new(vec![]);
+static ALLOWED_MODULES: Mutex<Vec<Option<&str>>> = Mutex::new(vec![]);
 
 // Statistics about what's actually getting executed during fuzzing
 static STATS: RuntimeStats = RuntimeStats::new();
@@ -73,7 +73,13 @@ fn execute_one(data: &[u8]) -> Result<()> {
     // Choose an engine that Wasmtime will be differentially executed against.
     // The chosen engine is then created, which might update `config`, and
     // returned as a trait object.
-    let lhs = u.choose(&allowed_engines)?;
+    let lhs = match *u.choose(&allowed_engines)? {
+        Some(engine) => engine,
+        None => {
+            log::debug!("test case uses a runtime-disabled engine");
+            return Ok(());
+        }
+    };
     let mut lhs = match engine::build(&mut u, lhs, &mut config)? {
         Some(engine) => engine,
         // The chosen engine does not have support compiled into the fuzzer,
@@ -100,8 +106,12 @@ fn execute_one(data: &[u8]) -> Result<()> {
         panic!("unable to generate a module to fuzz against; check `ALLOWED_MODULES`")
     }
     let wasm = match *u.choose(&allowed_modules)? {
-        "wasm-smith" => build_wasm_smith_module(&mut u, &config)?,
-        "single-inst" => build_single_inst_module(&mut u, &config)?,
+        Some("wasm-smith") => build_wasm_smith_module(&mut u, &config)?,
+        Some("single-inst") => build_single_inst_module(&mut u, &config)?,
+        None => {
+            log::debug!("test case uses a runtime-disabled module strategy");
+            return Ok(());
+        }
         _ => unreachable!(),
     };