diff --git a/src/core/package/diff/PackageDiffImpl.ts b/src/core/package/diff/PackageDiffImpl.ts
index 3764d16c3..d1e8f01ac 100644
--- a/src/core/package/diff/PackageDiffImpl.ts
+++ b/src/core/package/diff/PackageDiffImpl.ts
@@ -47,6 +47,10 @@ export default class PackageDiffImpl {
         let tag: string;
         if (!this.diffOptions?.useLatestGitTags && this.diffOptions?.packagesMappedToLastKnownCommitId != null) {
             tag = this.getLatestCommitFromMap(this.sfdx_package, this.diffOptions?.packagesMappedToLastKnownCommitId);
+        } else if (this.diffOptions?.useBranchCompare) {
+            // if branch compare is enabled, we will use the merge base as tag for the whole diff
+            tag = await git.raw(['merge-base', this.diffOptions.branch, this.diffOptions.baseBranch]);
+            tag = tag.trim();
         } else {
             tag = await this.getLatestTagFromGit(git, this.sfdx_package);
         }
@@ -57,19 +61,18 @@ export default class PackageDiffImpl {
             // Get the list of modified files between the tag and HEAD refs
             let modified_files: string[];
             try {
-                if(this.diffOptions?.useBranchCompare)
-                {
-                 const mergeBase = await git.raw(['merge-base', this.diffOptions.branch, this.diffOptions.baseBranch]);
-                 modified_files = await git.diff(['--no-renames','--name-only', this.diffOptions.branch, mergeBase.trim()]);
+                let targetref: string;
+                if(this.diffOptions?.useBranchCompare) {
+                    targetref = this.diffOptions.branch;
                 }
-                else
-                {
-                 modified_files = await git.diff([`${tag}`, `HEAD`, `--no-renames`, `--name-only`]);
+                else {
+                    targetref = `HEAD`;
                 }
+                modified_files = await git.diff([`${tag}`, `${targetref}`, `--no-renames`, `--name-only`]);
             } catch (error) {
                 if(this.diffOptions?.fallBackToNoTag)
                 {
-                    SFPLogger.log(COLOR_WARNING(dedent(`Unable to compute diff, 
+                    SFPLogger.log(COLOR_WARNING(dedent(`Unable to compute diff,
                     The head of the branch is not reachable from the commit id ${tag} for ${this.sfdx_package}
                     Attempting to build the package without diffing against the previous version`)),LoggerLevel.INFO,this.logger);
                     return { isToBeBuilt: true, reason: `Previous version is from an earlier branch` };
@@ -96,12 +99,12 @@ export default class PackageDiffImpl {
 
             // Check whether the package has been modified
             for (let filename of modified_files) {
-                
+
                 let normalizedPkgPath = path.normalize(pkgDescriptor.path);
                 let normalizedFilename = path.normalize(filename);
-            
+
                 let relativePath = path.relative(normalizedPkgPath, normalizedFilename);
-            
+
                 if (!relativePath.startsWith('..')) {
                     SFPLogger.log(`Found change(s) in ${filename}`, LoggerLevel.TRACE, this.logger);
                     return { isToBeBuilt: true, reason: `Found change(s) in package`, tag: tag };
@@ -128,12 +131,12 @@ export default class PackageDiffImpl {
 
                  // Check whether the package has been modified
                 for (let filename of modified_files) {
-                        
+
                     let normalizedPkgPath = path.normalize(pkgDescriptor.path);
                     let normalizedFilename = path.normalize(filename);
-                
+
                     let relativePath = path.relative(normalizedPkgPath, normalizedFilename);
-                
+
                     if (!relativePath.startsWith('..')) {
                         SFPLogger.log(`Found change(s) in ${filename}`, LoggerLevel.TRACE, this.logger);
                         return { isToBeBuilt: true, reason: `Found change(s) in package`, tag: tag };