diff --git a/src/asciicast.rs b/src/asciicast.rs
index 6ffc347..98e9121 100644
--- a/src/asciicast.rs
+++ b/src/asciicast.rs
@@ -274,6 +274,11 @@ mod tests {
         assert_eq!(version, 1);
         assert_eq!((header.term_cols, header.term_rows), (100, 50));
 
+        let mut expected_env = HashMap::new();
+        expected_env.insert("SHELL".to_owned(), "/bin/bash".to_owned());
+        expected_env.insert("TERM".to_owned(), "xterm-256color".to_owned());
+        assert_eq!(header.env.unwrap(), expected_env);
+
         assert_eq!(events[0].time, Duration::from_micros(1));
         assert!(matches!(events[0].data, EventData::Output(ref s) if s == "ż"));
 
@@ -284,6 +289,18 @@ mod tests {
         assert!(matches!(events[2].data, EventData::Output(ref s) if s == "\r\n"));
     }
 
+    #[test]
+    fn open_v1_with_nulls_in_header() {
+        let Asciicast {
+            version, header, ..
+        } = super::open_from_path("tests/casts/nulls-v1.json").unwrap();
+        assert_eq!(version, 1);
+
+        let mut expected_env = HashMap::new();
+        expected_env.insert("SHELL".to_owned(), "/bin/bash".to_owned());
+        assert_eq!(header.env.unwrap(), expected_env);
+    }
+
     #[test]
     fn open_v2_minimal() {
         let Asciicast {
@@ -319,6 +336,11 @@ mod tests {
         assert_eq!(theme.bg, RGB8::new(0xff, 0xff, 0xff));
         assert_eq!(theme.palette[0], RGB8::new(0x24, 0x1f, 0x31));
 
+        let mut expected_env = HashMap::new();
+        expected_env.insert("SHELL".to_owned(), "/bin/bash".to_owned());
+        expected_env.insert("TERM".to_owned(), "xterm-256color".to_owned());
+        assert_eq!(header.env.unwrap(), expected_env);
+
         assert_eq!(events[0].time, Duration::from_micros(1));
         assert!(matches!(events[0].data, EventData::Output(ref s) if s == "ż"));
 
@@ -338,6 +360,18 @@ mod tests {
         assert!(matches!(events[4].data, EventData::Output(ref s) if s == "\r\n"));
     }
 
+    #[test]
+    fn open_v2_with_nulls_in_header() {
+        let Asciicast {
+            version, header, ..
+        } = super::open_from_path("tests/casts/nulls-v2.cast").unwrap();
+        assert_eq!(version, 2);
+
+        let mut expected_env = HashMap::new();
+        expected_env.insert("SHELL".to_owned(), "/bin/bash".to_owned());
+        assert_eq!(header.env.unwrap(), expected_env);
+    }
+
     #[test]
     fn open_v3_minimal() {
         let Asciicast {
diff --git a/src/asciicast/v1.rs b/src/asciicast/v1.rs
index e2b6124..ebb696e 100644
--- a/src/asciicast/v1.rs
+++ b/src/asciicast/v1.rs
@@ -14,7 +14,7 @@ struct V1 {
     height: u16,
     command: Option<String>,
     title: Option<String>,
-    env: Option<HashMap<String, String>>,
+    env: Option<HashMap<String, Option<String>>>,
     stdout: Vec<V1OutputEvent>,
 }
 
@@ -35,8 +35,16 @@ pub fn load(json: String) -> Result<Asciicast<'static>> {
     let term_type = asciicast
         .env
         .as_ref()
-        .and_then(|env| env.get("TERM"))
-        .cloned();
+        .map(|env| env.get("TERM"))
+        .unwrap_or_default()
+        .cloned()
+        .unwrap_or_default();
+
+    let env = asciicast.env.map(|env| {
+        env.into_iter()
+            .filter_map(|(k, v)| v.map(|v| (k, v)))
+            .collect()
+    });
 
     let header = Header {
         term_cols: asciicast.width,
@@ -48,7 +56,7 @@ pub fn load(json: String) -> Result<Asciicast<'static>> {
         idle_time_limit: None,
         command: asciicast.command.clone(),
         title: asciicast.title.clone(),
-        env: asciicast.env.clone(),
+        env,
     };
 
     let events = Box::new(asciicast.stdout.into_iter().scan(
diff --git a/src/asciicast/v2.rs b/src/asciicast/v2.rs
index 848f304..bd3358c 100644
--- a/src/asciicast/v2.rs
+++ b/src/asciicast/v2.rs
@@ -18,7 +18,7 @@ struct V2Header {
     idle_time_limit: Option<f64>,
     command: Option<String>,
     title: Option<String>,
-    env: Option<HashMap<String, String>>,
+    env: Option<HashMap<String, Option<String>>>,
     theme: Option<V2Theme>,
 }
 
@@ -70,9 +70,22 @@ pub fn open(header_line: &str) -> Result<Parser> {
 
 impl Parser {
     pub fn parse<'a, I: Iterator<Item = io::Result<String>> + 'a>(self, lines: I) -> Asciicast<'a> {
-        let term_type = self.0.env.as_ref().and_then(|env| env.get("TERM").cloned());
+        let term_type = self
+            .0
+            .env
+            .as_ref()
+            .map(|env| env.get("TERM").cloned())
+            .unwrap_or_default()
+            .unwrap_or_default();
+
         let term_theme = self.0.theme.as_ref().map(|t| t.into());
 
+        let env = self.0.env.map(|env| {
+            env.into_iter()
+                .filter_map(|(k, v)| v.map(|v| (k, v)))
+                .collect()
+        });
+
         let header = Header {
             term_cols: self.0.width,
             term_rows: self.0.height,
@@ -83,7 +96,7 @@ impl Parser {
             idle_time_limit: self.0.idle_time_limit,
             command: self.0.command.clone(),
             title: self.0.title.clone(),
-            env: self.0.env.clone(),
+            env,
         };
 
         let events = Box::new(lines.filter_map(parse_line));
@@ -367,6 +380,11 @@ impl serde::Serialize for V2Palette {
 
 impl From<&Header> for V2Header {
     fn from(header: &Header) -> Self {
+        let env = header
+            .env
+            .clone()
+            .map(|env| env.into_iter().map(|(k, v)| (k, Some(v))).collect());
+
         V2Header {
             version: 2,
             width: header.term_cols,
@@ -375,7 +393,7 @@ impl From<&Header> for V2Header {
             idle_time_limit: header.idle_time_limit,
             command: header.command.clone(),
             title: header.title.clone(),
-            env: header.env.clone(),
+            env,
             theme: header.term_theme.as_ref().map(|t| t.into()),
         }
     }
diff --git a/tests/casts/nulls-v1.json b/tests/casts/nulls-v1.json
new file mode 100644
index 0000000..0982c1b
--- /dev/null
+++ b/tests/casts/nulls-v1.json
@@ -0,0 +1,15 @@
+{
+  "version": 1,
+  "width": 100,
+  "height": 50,
+  "env": {
+    "SHELL": "/bin/bash",
+    "TERM": null
+  },
+  "stdout": [
+    [
+      1.230000,
+      "hello"
+    ]
+  ]
+}
diff --git a/tests/casts/nulls-v2.cast b/tests/casts/nulls-v2.cast
new file mode 100644
index 0000000..afd225c
--- /dev/null
+++ b/tests/casts/nulls-v2.cast
@@ -0,0 +1,2 @@
+{"version":2,"width":100,"height":50,"env":{"TERM":null,"SHELL":"/bin/bash"}}
+[1.23, "o", "hello"]