diff --git a/src/analyze/BuildSystem.re b/src/analyze/BuildSystem.re
index e11fe52b..628ea5e2 100644
--- a/src/analyze/BuildSystem.re
+++ b/src/analyze/BuildSystem.re
@@ -264,10 +264,24 @@ let isRunningInEsyNamedSandbox = () => {
 };
 
 let getExecutableInEsyPath = (exeName, ~pwd) => {
-  if (isRunningInEsyNamedSandbox()) {
+  let ret = if (isRunningInEsyNamedSandbox()) {
     getLine("which " ++ exeName, ~pwd)
   } else {
     getLine("esy which " ++ exeName, ~pwd)
+  };
+  if (Sys.win32) {
+    switch ret {
+      | RResult.Ok(ret) =>
+        let ret = if (isRunningInEsyNamedSandbox()) {
+          getLine("cygpath -w " ++ ret, ~pwd)
+        } else {
+          getLine("esy cygpath -w " ++ ret, ~pwd)
+        };
+        ret
+      | Error(a) => Error(a)
+    }
+  } else {
+    ret
   }
 };
 
diff --git a/src/analyze/Packages.re b/src/analyze/Packages.re
index ae2546ad..aec063a1 100644
--- a/src/analyze/Packages.re
+++ b/src/analyze/Packages.re
@@ -362,7 +362,9 @@ let newJbuilderPackage = (~overrideBuildSystem=?, ~reportDiagnostics, state, roo
 
 
     /* Log.log("Getting things"); */
-    let (otherDirectories, otherFiles) = source |> List.filter(s => s != "." && s != "" && s.[0] != '/') |> optMap(name => {
+    let (globalSource, localSource) = List.filter(s => s != "." && s != "", source)
+    |> List.partition(Infix.isFullPath);
+    let (otherDirectories, otherFiles) = localSource |> optMap(name => {
       let otherPath = rootPath /+ name;
       let res = {
         let%try (jbuildPath, jbuildRaw) = JbuildFile.readFromDir(otherPath);
@@ -395,7 +397,7 @@ let newJbuilderPackage = (~overrideBuildSystem=?, ~reportDiagnostics, state, roo
       }
     }) |> List.split;
 
-    let dependencyDirectories = (source |> List.filter(s => s != "" && s != "." && s.[0] == '/')) @ stdlibs;
+    let dependencyDirectories = globalSource @ stdlibs;
 
     let dependencyModules = dependencyDirectories
     |> List.map(path => {
diff --git a/util/Files.re b/util/Files.re
index 9ed24efd..f712d6f2 100644
--- a/util/Files.re
+++ b/util/Files.re
@@ -4,7 +4,7 @@ let split = (str, string) => Str.split(Str.regexp_string(str), string);
 let absify = path => {
   if (path == "" || path == ".") {
     Unix.getcwd()
-  } else if (path.[0] == '/') {
+  } else if (Infix.isFullPath(path)) {
     path
   } else {
     Filename.concat(Unix.getcwd(), path)
diff --git a/util/Infix.re b/util/Infix.re
index 14e64d8b..4f737f02 100644
--- a/util/Infix.re
+++ b/util/Infix.re
@@ -33,8 +33,10 @@ let logIfAbsent = (message, x) => switch x {
   | _ => x
 };
 
+let isFullPath = b => b.[0] == '/' || Sys.win32 && String.length(b) > 1 && b.[1] == ':';
+
 let maybeConcat = (a, b) => {
-  if (b != "" && b.[0] == '/') {
+  if (b != "" && isFullPath(b)) {
     b
   } else {
     fileConcat(a, b)
diff --git a/util/MerlinFile.re b/util/MerlinFile.re
index dd815981..2e8535d6 100644
--- a/util/MerlinFile.re
+++ b/util/MerlinFile.re
@@ -33,10 +33,10 @@ let parseMerlin = (base, text) => {
   )
 };
 
-// let maybeConcat = (base, path) => path.[0] == '/' ? path : Filename.concat(base, path);
+// let maybeConcat = (base, path) => Infix.isFullPath(path) ? path : Filename.concat(base, path);
 
-let isRelativePath = Sys.os_type == "Win32"
-? path => !Str.string_match(Str.regexp("[A-Z]:"), path, 0)
+let isRelativePath = Sys.win32
+? path => !Str.string_match(Str.regexp("[A-Za-z]:"), path, 0)
 : path => path != "" && path.[0] != '/';
 
 let isBuildFile = name =>