diff --git a/src/uu/cp/src/cp.rs b/src/uu/cp/src/cp.rs
index 046ac6a8730..639babccb9c 100644
--- a/src/uu/cp/src/cp.rs
+++ b/src/uu/cp/src/cp.rs
@@ -1482,7 +1482,7 @@ pub fn copy(sources: &[PathBuf], target: &Path, options: &Options) -> CopyResult
 
     for source in sources {
         let normalized_source = normalize_path(source);
-        if options.backup == BackupMode::None && seen_sources.contains(&normalized_source) {
+        if options.backup == BackupMode::None && !seen_sources.insert(normalized_source) {
             let file_type = if source.symlink_metadata()?.file_type().is_dir() {
                 "directory"
             } else {
@@ -1538,7 +1538,6 @@ pub fn copy(sources: &[PathBuf], target: &Path, options: &Options) -> CopyResult
                 copied_destinations.insert(dest.clone());
             }
         }
-        seen_sources.insert(normalized_source);
     }
 
     if let Some(pb) = progress_bar {
diff --git a/src/uu/du/src/du.rs b/src/uu/du/src/du.rs
index 4cbd67ddc49..48dff14064f 100644
--- a/src/uu/du/src/du.rs
+++ b/src/uu/du/src/du.rs
@@ -538,11 +538,11 @@ fn safe_du(
         }
 
         // Handle inodes
-        if let Some(inode) = this_stat.inode {
-            if seen_inodes.contains(&inode) && !options.count_links {
-                continue;
-            }
-            seen_inodes.insert(inode);
+        if let Some(inode) = this_stat.inode
+            && !seen_inodes.insert(inode)
+            && !options.count_links
+        {
+            continue;
         }
 
         // Process directories recursively
@@ -702,14 +702,11 @@ fn du_regular(
                                 }
                             }
 
-                            if let Some(inode) = this_stat.inode {
-                                // Check if the inode has been seen before and if we should skip it
-                                if seen_inodes.contains(&inode) && !options.count_links {
-                                    // Skip further processing for this inode
-                                    continue;
-                                }
-                                // Mark this inode as seen
-                                seen_inodes.insert(inode);
+                            if let Some(inode) = this_stat.inode
+                                && !seen_inodes.insert(inode)
+                                && !options.count_links
+                            {
+                                continue;
                             }
 
                             if this_stat.metadata.is_dir() {
@@ -1202,11 +1199,10 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
         let stat = Stat::new(&path, None, &traversal_options);
         if let Ok(stat) = stat.as_ref()
             && let Some(inode) = stat.inode
+            && !traversal_options.count_links
+            && !seen_inodes.insert(inode)
         {
-            if !traversal_options.count_links && seen_inodes.contains(&inode) {
-                continue 'loop_file;
-            }
-            seen_inodes.insert(inode);
+            continue 'loop_file;
         }
 
         if use_safe_traversal {
diff --git a/src/uu/hostname/src/hostname.rs b/src/uu/hostname/src/hostname.rs
index da1adeb58ac..1c06c944335 100644
--- a/src/uu/hostname/src/hostname.rs
+++ b/src/uu/hostname/src/hostname.rs
@@ -101,7 +101,7 @@ fn display_hostname(matches: &ArgMatches) -> UResult<()> {
         let mut output = String::new();
         for addr in addresses {
             // XXX: not sure why this is necessary...
-            if !hashset.contains(&addr) {
+            if hashset.insert(addr) {
                 let mut ip = addr.to_string();
                 if ip.ends_with(":1") {
                     let len = ip.len();
@@ -109,7 +109,6 @@ fn display_hostname(matches: &ArgMatches) -> UResult<()> {
                 }
                 output.push_str(&ip);
                 output.push(' ');
-                hashset.insert(addr);
             }
         }
         let len = output.len();