diff --git a/modrinth/install.go b/modrinth/install.go
index 4adb2c8..a146ca8 100644
--- a/modrinth/install.go
+++ b/modrinth/install.go
@@ -39,9 +39,17 @@ var installCmd = &cobra.Command{
 		var projectID, versionID, versionFilename string
 		if projectIDFlag != "" {
 			projectID = projectIDFlag
+			if len(args) != 0 {
+				fmt.Println("--project-id cannot be used with a separately specified URL/slug/search term")
+				os.Exit(1)
+			}
 		}
 		if versionIDFlag != "" {
 			versionID = versionIDFlag
+			if len(args) != 0 {
+				fmt.Println("--version-id cannot be used with a separately specified URL/slug/search term")
+				os.Exit(1)
+			}
 		}
 		if versionFilenameFlag != "" {
 			versionFilename = versionFilenameFlag
@@ -52,17 +60,15 @@ var installCmd = &cobra.Command{
 			os.Exit(1)
 		}
 
-		// Try interpreting the argument as a slug/project ID, or project/version/CDN URL
 		var version string
-		parsedSlug, err := parseSlugOrUrl(args[0], &projectID, &version, &versionID, &versionFilename)
-		if err != nil {
-			fmt.Printf("Failed to parse URL: %v\n", err)
-			os.Exit(1)
-		}
-
-		if version != "" && versionID == "" {
-			// TODO: resolve version (could be an ID, could be a version number) into ID
-			versionID = version
+		var parsedSlug bool
+		if projectID == "" && versionID == "" {
+			// Try interpreting the argument as a slug/project ID, or project/version/CDN URL
+			parsedSlug, err = parseSlugOrUrl(args[0], &projectID, &version, &versionID, &versionFilename)
+			if err != nil {
+				fmt.Printf("Failed to parse URL: %v\n", err)
+				os.Exit(1)
+			}
 		}
 
 		// Got version ID; install using this ID
@@ -82,6 +88,22 @@ var installCmd = &cobra.Command{
 			project, err = mrDefaultClient.Projects.Get(projectID)
 			if err == nil {
 				// We found a project with that id/slug
+				if version != "" {
+					// Try to look up version number
+					versionData, err := resolveVersion(project, version)
+					if err != nil {
+						fmt.Printf("Failed to add project: %s\n", err)
+						os.Exit(1)
+					}
+					err = installVersion(project, versionData, versionFilename, pack, &index)
+					if err != nil {
+						fmt.Printf("Failed to add project: %s\n", err)
+						os.Exit(1)
+					}
+					return
+				}
+
+				// No version specified; find latest
 				err = installProject(project, versionFilename, pack, &index)
 				if err != nil {
 					fmt.Printf("Failed to add project: %s\n", err)
diff --git a/modrinth/modrinth.go b/modrinth/modrinth.go
index 2fb01e6..c2fc453 100644
--- a/modrinth/modrinth.go
+++ b/modrinth/modrinth.go
@@ -341,3 +341,27 @@ func getInstalledProjectIDs(index *core.Index) []string {
 	}
 	return installedProjects
 }
+
+func resolveVersion(project *modrinthApi.Project, version string) (*modrinthApi.Version, error) {
+	// If it exists in the version list, it is already a version ID (and doesn't need querying further)
+	if slices.Contains(project.Versions, version) {
+		versionData, err := mrDefaultClient.Versions.Get(version)
+		if err != nil {
+			return nil, fmt.Errorf("failed to fetch version %s: %v", version, err)
+		}
+		return versionData, nil
+	}
+
+	// Look up all versions
+	// TODO: PR a version number filter to Modrinth?
+	versionsList, err := mrDefaultClient.Versions.ListVersions(*project.ID, modrinthApi.ListVersionsOptions{})
+	if err != nil {
+		return nil, fmt.Errorf("failed to fetch version list for %s: %v", *project.ID, err)
+	}
+	for _, v := range versionsList {
+		if *v.VersionNumber == version {
+			return v, nil
+		}
+	}
+	return nil, fmt.Errorf("unable to find version %s", version)
+}