diff --git a/library/std/src/sys/args/zkvm.rs b/library/std/src/sys/args/zkvm.rs
index d26bf1eaff91f..603ef4017097e 100644
--- a/library/std/src/sys/args/zkvm.rs
+++ b/library/std/src/sys/args/zkvm.rs
@@ -16,11 +16,14 @@ fn get_args() -> Vec<&'static OsStr> {
         // Get the size of the argument then the data.
         let arg_len = unsafe { abi::sys_argv(ptr::null_mut(), 0, i) };
 
-        let arg_len_words = (arg_len + WORD_SIZE - 1) / WORD_SIZE;
+        let arg_len_rounded =
+            arg_len.checked_next_multiple_of(WORD_SIZE).expect("argument length overflowed");
+        assert!(arg_len_rounded <= isize::MAX as usize, "argument length is too large");
+        let arg_len_words = arg_len_rounded / WORD_SIZE;
         let words = unsafe { abi::sys_alloc_words(arg_len_words) };
 
         let arg_len2 = unsafe { abi::sys_argv(words, arg_len_words, i) };
-        debug_assert_eq!(arg_len, arg_len2);
+        assert_eq!(arg_len, arg_len2);
 
         let arg_bytes = unsafe { slice::from_raw_parts(words.cast(), arg_len) };
         args.push(unsafe { OsStr::from_encoded_bytes_unchecked(arg_bytes) });
diff --git a/library/std/src/sys/env/zkvm.rs b/library/std/src/sys/env/zkvm.rs
index b672a03bf0ba7..ef45d73d3511b 100644
--- a/library/std/src/sys/env/zkvm.rs
+++ b/library/std/src/sys/env/zkvm.rs
@@ -15,11 +15,14 @@ pub fn getenv(varname: &OsStr) -> Option<OsString> {
         return None;
     }
 
-    let nwords = (nbytes + WORD_SIZE - 1) / WORD_SIZE;
+    let nbytes_rounded =
+        nbytes.checked_next_multiple_of(WORD_SIZE).expect("environment variable length overflowed");
+    assert!(nbytes_rounded <= isize::MAX as usize, "environment variable length is too large");
+    let nwords = nbytes_rounded / WORD_SIZE;
     let words = unsafe { abi::sys_alloc_words(nwords) };
 
     let nbytes2 = unsafe { abi::sys_getenv(words, nwords, varname.as_ptr(), varname.len()) };
-    debug_assert_eq!(nbytes, nbytes2);
+    assert_eq!(nbytes, nbytes2);
 
     // Convert to OsString.
     //