diff --git a/src/commands/commit.rs b/src/commands/commit.rs
index 8c02e38..95e2dc4 100644
--- a/src/commands/commit.rs
+++ b/src/commands/commit.rs
@@ -350,8 +350,23 @@ impl CommitCommand {
             .output()?;
 
         if !output.status.success() {
+            let stdout = String::from_utf8_lossy(&output.stdout);
             let stderr = String::from_utf8_lossy(&output.stderr);
-            bail!("Failed to amend commit: {}", stderr);
+            
+            let error_msg = if stderr.is_empty() {
+                if stdout.is_empty() {
+                    "GPG signing failed. Please check:\n\
+                     1. GPG signing key is configured (git config --get user.signingkey)\n\
+                     2. GPG agent is running\n\
+                     3. You can sign commits manually (try: git commit --amend -S)".to_string()
+                } else {
+                    stdout.to_string()
+                }
+            } else {
+                stderr.to_string()
+            };
+            
+            bail!("Failed to amend commit: {}", error_msg);
         }
 
         Ok(())
diff --git a/src/git/commit.rs b/src/git/commit.rs
index 53da566..1807025 100644
--- a/src/git/commit.rs
+++ b/src/git/commit.rs
@@ -174,8 +174,23 @@ impl CommitBuilder {
             .output()?;
         
         if !output.status.success() {
+            let stdout = String::from_utf8_lossy(&output.stdout);
             let stderr = String::from_utf8_lossy(&output.stderr);
-            bail!("Failed to amend commit: {}", stderr);
+            
+            let error_msg = if stderr.is_empty() {
+                if stdout.is_empty() {
+                    "GPG signing failed. Please check:\n\
+                     1. GPG signing key is configured (git config --get user.signingkey)\n\
+                     2. GPG agent is running\n\
+                     3. You can sign commits manually (try: git commit --amend -S)".to_string()
+                } else {
+                    stdout.to_string()
+                }
+            } else {
+                stderr.to_string()
+            };
+            
+            bail!("Failed to amend commit: {}", error_msg);
         }
         
         Ok(())
diff --git a/src/git/mod.rs b/src/git/mod.rs
index 3442b58..de4882e 100644
--- a/src/git/mod.rs
+++ b/src/git/mod.rs
@@ -374,8 +374,23 @@ impl GitRepo {
             .output()?;
 
         if !output.status.success() {
+            let stdout = String::from_utf8_lossy(&output.stdout);
             let stderr = String::from_utf8_lossy(&output.stderr);
-            bail!("Failed to create signed commit: {}", stderr);
+            
+            let error_msg = if stderr.is_empty() {
+                if stdout.is_empty() {
+                    "GPG signing failed. Please check:\n\
+                     1. GPG signing key is configured (git config --get user.signingkey)\n\
+                     2. GPG agent is running\n\
+                     3. You can sign commits manually (try: git commit -S -m 'test')".to_string()
+                } else {
+                    stdout.to_string()
+                }
+            } else {
+                stderr.to_string()
+            };
+            
+            bail!("Failed to create signed commit: {}", error_msg);
         }
 
         let head = self.repo.head()?;