diff --git a/nvm.sh b/nvm.sh
index 4332e08..b1cf64c 100755
--- a/nvm.sh
+++ b/nvm.sh
@@ -3332,10 +3332,10 @@ nvm() {
       nvm_err "\${HOME}: ${HOME}"
       nvm_err "\${NVM_DIR}: '$(nvm_sanitize_path "${NVM_DIR}")'"
       nvm_err "\${PATH}: $(nvm_sanitize_path "${PATH}")"
-      nvm_err "\$PREFIX: '$(nvm_sanitize_path "${PREFIX}")'"
-      nvm_err "\${NPM_CONFIG_PREFIX}: '$(nvm_sanitize_path "${NPM_CONFIG_PREFIX}")'"
-      nvm_err "\$NVM_NODEJS_ORG_MIRROR: '${NVM_NODEJS_ORG_MIRROR}'"
-      nvm_err "\$NVM_IOJS_ORG_MIRROR: '${NVM_IOJS_ORG_MIRROR}'"
+      nvm_err "\$PREFIX: '$(nvm_sanitize_path "${PREFIX-}")'"
+      nvm_err "\${NPM_CONFIG_PREFIX}: '$(nvm_sanitize_path "${NPM_CONFIG_PREFIX-}")'"
+      nvm_err "\$NVM_NODEJS_ORG_MIRROR: '${NVM_NODEJS_ORG_MIRROR-}'"
+      nvm_err "\$NVM_IOJS_ORG_MIRROR: '${NVM_IOJS_ORG_MIRROR-}'"
       nvm_err "shell version: '$(${SHELL} --version | command head -n 1)'"
       nvm_err "uname -a: '$(command uname -a | command awk '{$2=""; print}' | command xargs)'"
       nvm_err "checksum binary: '$(nvm_get_checksum_binary 2>/dev/null)'"