diff --git a/install.ps1 b/install.ps1
index dc4cdce..bcc124b 100644
--- a/install.ps1
+++ b/install.ps1
@@ -6,7 +6,7 @@ param(
     [string]$DoshHost = $(if ($env:DOSH_HOST) { $env:DOSH_HOST } else { $env:DOSH_DOSH_HOST }),
     [int]$Port = $(if ($env:DOSH_PORT) { [int]$env:DOSH_PORT } else { 50000 }),
     [string]$Prefix = $(if ($env:PREFIX) { $env:PREFIX } else { Join-Path $HOME ".local" }),
-    [switch]$UsePrebuilt = $($env:DOSH_USE_PREBUILT -and $env:DOSH_USE_PREBUILT -ne "0"),
+    [switch]$UsePrebuilt = $(-not $env:DOSH_USE_PREBUILT -or $env:DOSH_USE_PREBUILT -ne "0"),
     [string]$BinaryUrl = $env:DOSH_BINARY_URL,
     [string]$BinaryBase = $env:DOSH_BINARY_BASE,
     [string]$BinaryName = $env:DOSH_BINARY_NAME,
diff --git a/install.sh b/install.sh
index ecbfb9a..e249cb7 100755
--- a/install.sh
+++ b/install.sh
@@ -12,7 +12,7 @@ start_server=1
 force_config=0
 update_cache="${DOSH_UPDATE_CACHE:-$HOME/.cache/dosh/source}"
 quiet="${DOSH_UPDATE_QUIET:-0}"
-use_prebuilt="${DOSH_USE_PREBUILT:-0}"
+use_prebuilt="${DOSH_USE_PREBUILT:-1}"
 binary_url="${DOSH_BINARY_URL:-}"
 binary_base="${DOSH_BINARY_BASE:-}"
 binary_name="${DOSH_BINARY_NAME:-}"
@@ -38,8 +38,8 @@ Options:
 Environment alternatives:
   DOSH_REPO, DOSH_ROLE, DOSH_SERVER, DOSH_HOST, DOSH_PORT, PREFIX,
   DOSH_UPDATE_CACHE
-  DOSH_USE_PREBUILT=1
-                  Try a release tarball before building from source
+  DOSH_USE_PREBUILT=0
+                  Build from source instead of trying a release tarball first
   DOSH_BINARY_URL URL
                   Exact release tarball URL to install
   DOSH_BINARY_BASE URL