diff --git a/src/package-modules.js b/src/package-modules.js
index 680a747..ef70f28 100644
--- a/src/package-modules.js
+++ b/src/package-modules.js
@@ -94,6 +94,18 @@ function chooseNameAndVersion(magentoName, composerJson, ref, givenVersion) {
   const composerConfig = JSON.parse(composerJson);
   let {version, name} = composerConfig;
   version = givenVersion || version;
+  
+  // If no version is found and ref looks like a branch name, convert to dev-branch format
+  if (!version && ref && !ref.match(/^v?\d+\.\d+/)) {
+    version = `dev-${ref}`;
+  }
+  
+  // ALWAYS convert invalid version strings that are branch names to dev-branch format
+  // This catches cases where composer.json itself contains "develop" as version
+  if (version && !version.match(/^v?\d+\.\d+/) && !version.startsWith('dev-') && version.match(/^[a-zA-Z][a-zA-Z0-9_-]*$/)) {
+    version = `dev-${version}`;
+  }
+  
   if (!name) {
     throw {
       kind: 'NAME_UNKNOWN',
@@ -166,7 +178,11 @@ async function determinePackageForRef(url, moduleDir, ref, options) {
     // Some refs do not have a version in the composer.json (e.g. the base package or the magento-composer-installer 0.4.0-beta1=
     // For those we use the ref as the version. This might be a problem, so for now we leave it as is.
     if (exception.kind === 'VERSION_UNKNOWN') {
-      return {[exception.name]: exception.ref}
+      // For branch names, convert to Composer dev- format
+      const version = exception.ref.match(/^v?(?:\d+\.){0,3}\d+(?:-[a-z]\w*|)$/i) 
+        ? exception.ref 
+        : `dev-${exception.ref}`;
+      return {[exception.name]: version}
     }
     console.log(`Unable to determine name and/or version for ${magentoName || url} in ${ref}: ${exception.message || exception}`);
     return {};
@@ -375,7 +391,18 @@ async function createComposerJsonOnlyPackage(url, ref, name, transform, release)
     isExecutable: false,
   }];
 
-  const packageFilepath = archiveFilePath(name, release || ref);
+  // Convert branch names to proper dev-branch format for Composer
+  let versionForFilename = release || ref;
+  if (!release && ref && !ref.match(/^v?\d+\.\d+/)) {
+    versionForFilename = `dev-${ref}`;
+  }
+  
+  // Also check if versionForFilename looks like a branch name and convert it
+  if (versionForFilename && !versionForFilename.match(/^v?\d+\.\d+/) && !versionForFilename.startsWith('dev-')) {
+    versionForFilename = `dev-${versionForFilename}`;
+  }
+
+  const packageFilepath = archiveFilePath(name, versionForFilename);
   return {packageFilepath, files}
 }
 
@@ -587,6 +614,11 @@ async function determineMetaPackageFromRepoDir(url, dir, ref, release) {
     throw {message: `Unable find package name and in composer.json for metapackage ${ref} in ${dir}`}
   }
   version = release || version || ref;
+  
+  // If no version is found and ref looks like a branch name, convert to dev-branch format
+  if (!release && !composerConfig.version && ref && !ref.match(/^v?\d+\.\d+/)) {
+    version = `dev-${ref}`;
+  }
 
   return {[name]: version}
 }
@@ -613,6 +645,11 @@ async function createMetaPackageFromRepoDir(url, dir, ref, options) {
     throw {message: `Unable find package name and in composer.json for metapackage ${ref} in ${dir}`}
   }
   version = release || dependencyVersions[name] || version || ref;
+  
+  // If no version is found and ref looks like a branch name, convert to dev-branch format
+  if (!release && !dependencyVersions[name] && !composerConfig.version && ref && !ref.match(/^v?\d+\.\d+/)) {
+    version = `dev-${ref}`;
+  }
 
   // Ensure version is set on composer config because not all repos provide the version in composer.json (e.g.
   // page-builder) and it is required by satis to be able to use artifact repositories.
diff --git a/src/release-branch-build-tools.js b/src/release-branch-build-tools.js
index 1c1c71c..2923107 100644
--- a/src/release-branch-build-tools.js
+++ b/src/release-branch-build-tools.js
@@ -81,6 +81,11 @@ async function getPackageVersionsForBuildInstructions(buildInstructions, suffix)
 }
 
 function addSuffixToVersion(version, buildSuffix) {
+  // Don't add suffix to dev- branch versions
+  if (version.startsWith('dev-')) {
+    return version;
+  }
+
   const match = version.match(/(?<versions>(?:[\d]+\.?){1,4})(?<suffix>-[^+]+)?(?<legacy>\+.+)?/)
   if (match) {
     return `${match.groups.versions}-a${buildSuffix}${match.groups.legacy ? match.groups.legacy : ''}`
@@ -100,6 +105,11 @@ function transformVersionsToNightlyBuildVersion(baseVersion, buildSuffix) {
 }
 
 function calcNightlyBuildPackageBaseVersion(version) {
+  // Handle dev- branch versions (e.g., dev-develop, dev-master)
+  if (version.startsWith('dev-')) {
+    return version; // Return as-is, it's already a valid Composer branch version
+  }
+
   if (! version.match(/^v?(?:\d+\.){0,3}\d+(?:-[a-z]\w*|)$/i)) {
     throw Error(`Unable to determine branch release version for input version "${version}"`)
   }