diff --git a/R/compile_imports.R b/R/compile_imports.R
index b20379b..d6715b1 100644
--- a/R/compile_imports.R
+++ b/R/compile_imports.R
@@ -10,7 +10,8 @@
   importsFormat <- data.frame(list(
     package_name = unlist(lapply(missingImports$package, format_str, width = 35)),
     req_ver = unlist(lapply(missingImports$req_version, format_str, width = 12)),
-    cran_ver = unlist(lapply(missingImports$cran_version, format_str, width = 12))
+    cran_ver = unlist(lapply(missingImports$cran_version, format_str, width = 12)),
+    stringsAsFactors = FALSE
   ))
 
   cat("\n")
diff --git a/R/list_depends.R b/R/list_depends.R
index feef367..7d24ff5 100644
--- a/R/list_depends.R
+++ b/R/list_depends.R
@@ -27,7 +27,8 @@
     version = rep(packages$Version, nDepends),
     imports = unlist(lapply(seq_along(packages$Package), function(idx) {
       c(packages$Imports[[idx]], packages$LinkingTo[[idx]], packages$Depends[[idx]])
-    }))
+    })),
+    stringsAsFactors = FALSE
   )
   packages$min_version <- gsub(packages$imports, pattern = "[^ ]*( \\([=> ]*([^)]+)\\))?", replacement = "\\2")
   packages$min_version = ifelse(nchar(packages$min_version) == 0, NA_character_, packages$min_version)
@@ -38,7 +39,7 @@
   dependsNext <- sort(unique(dependsNext))
   if (length(dependsNext) > 0) {
     packagesNext <- .list_depends(dependsNext, gen + 1)
-    packages <- rbind(packages, packagesNext)
+    packages <- rbind(packages, packagesNext, stringsAsFactors = FALSE)
   }
 
   return(packages)