diff --git a/gen_input/templates/vm-vm_CORENAME.cpp.gtl b/gen_input/templates/vm-vm_CORENAME.cpp.gtl
index 4002097..22ca9e7 100644
--- a/gen_input/templates/vm-vm_CORENAME.cpp.gtl
+++ b/gen_input/templates/vm-vm_CORENAME.cpp.gtl
@@ -38,7 +38,9 @@
 #include <iss/llvm/vm_base.h>
 #include <util/logging.h>
 
+#ifndef FMT_HEADER_ONLY
 #define FMT_HEADER_ONLY
+#endif
 #include <fmt/format.h>
 
 #include <array>
diff --git a/incl/iss/arch/riscv_hart_msu_vp.h b/incl/iss/arch/riscv_hart_msu_vp.h
index 04d421f..1379746 100644
--- a/incl/iss/arch/riscv_hart_msu_vp.h
+++ b/incl/iss/arch/riscv_hart_msu_vp.h
@@ -40,7 +40,9 @@
 #include "iss/instrumentation_if.h"
 #include "iss/log_categories.h"
 #include "iss/vm_if.h"
+#ifndef FMT_HEADER_ONLY
 #define FMT_HEADER_ONLY
+#endif
 #include <fmt/format.h>
 #include <array>
 #include <elfio/elfio.hpp>
diff --git a/incl/iss/debugger/riscv_target_adapter.h b/incl/iss/debugger/riscv_target_adapter.h
index 97e4afe..32cded0 100644
--- a/incl/iss/debugger/riscv_target_adapter.h
+++ b/incl/iss/debugger/riscv_target_adapter.h
@@ -40,7 +40,9 @@
 
 #include <array>
 #include <memory>
+#ifndef FMT_HEADER_ONLY
 #define FMT_HEADER_ONLY
+#endif
 #include <fmt/format.h>
 #include <util/logging.h>
 
diff --git a/src/internal/vm_rv32gc.cpp b/src/internal/vm_rv32gc.cpp
index 8d58336..043a8bb 100644
--- a/src/internal/vm_rv32gc.cpp
+++ b/src/internal/vm_rv32gc.cpp
@@ -38,7 +38,9 @@
 #include <iss/llvm/vm_base.h>
 #include <util/logging.h>
 
+#ifndef FMT_HEADER_ONLY
 #define FMT_HEADER_ONLY
+#endif
 #include <fmt/format.h>
 
 #include <array>
diff --git a/src/internal/vm_rv32imac.cpp b/src/internal/vm_rv32imac.cpp
index e7f57af..92be814 100644
--- a/src/internal/vm_rv32imac.cpp
+++ b/src/internal/vm_rv32imac.cpp
@@ -38,7 +38,9 @@
 #include <iss/llvm/vm_base.h>
 #include <util/logging.h>
 
+#ifndef FMT_HEADER_ONLY
 #define FMT_HEADER_ONLY
+#endif
 #include <fmt/format.h>
 
 #include <array>
diff --git a/src/internal/vm_rv64gc.cpp b/src/internal/vm_rv64gc.cpp
index 6261ca7..26dbd67 100644
--- a/src/internal/vm_rv64gc.cpp
+++ b/src/internal/vm_rv64gc.cpp
@@ -38,7 +38,9 @@
 #include <iss/llvm/vm_base.h>
 #include <util/logging.h>
 
+#ifndef FMT_HEADER_ONLY
 #define FMT_HEADER_ONLY
+#endif
 #include <fmt/format.h>
 
 #include <array>
diff --git a/src/internal/vm_rv64i.cpp b/src/internal/vm_rv64i.cpp
index 37ea5e8..5048e36 100644
--- a/src/internal/vm_rv64i.cpp
+++ b/src/internal/vm_rv64i.cpp
@@ -38,7 +38,9 @@
 #include <iss/llvm/vm_base.h>
 #include <util/logging.h>
 
+#ifndef FMT_HEADER_ONLY
 #define FMT_HEADER_ONLY
+#endif
 #include <fmt/format.h>
 
 #include <array>